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THE  LIBRARIES 


OPTOMETRY  LIBRARY 


DOITATED   BY 


LEO      HIRSCHBERG 


Optometry       '17 


Ski-optometer  Master  Model  215 

Embodying  in  a  Single  Instrument,  in  Convenient  Form, 
Cylindrical  and  Spherical  Lenses,   in  Combination 
with  Appliances  for  Testing  and  Cor- 
recting Miiscvdar  Imbalance. 


Refraction  and 
Muscular  Imbalance 


As  Simplified 

Through  the   Use  of  the 

Ski-optometer 


By 
DANIEL  WOOLF 


/ 


WOOLF  INSTRUMENT  CORPORATION 

New  York:  516  Fifth  Avenue 


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iERiCELSY     \ 

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UNfVc«JlTY    Of 
CALIfORNiA 


OPTOMETRY  LIBRARY 


Copyright  1921 
By  WOOLF  INSTRUMENT  CORPORATION 


Published  by 

Theodore  S.  Holbrook 

New  York 


CONTENTS 

Chapter  I  Page 

SkI-OPTOMETER  CoNSTRUCTrON 1 

Convex  Spherical  Lenses... 2 

Operates  and  Indicates  Automatically 6 

Concave  Spherical  Lenses 7 

Chapter  II 

Cylindrical  Lenses 10 

Obtaining  Correct  Focus 11 

Why  Concave  Cylinders  Are  Used  Exclusively  14 

Transposition  of  Lenses >.•  14 

Chapter  III 

How  THE  Ski-optometer  Assists  in  Refraction  17 

The  Use  of  the  Ski-optometer  in  Skioscopy 17 

A  Simplified  Skioscopic  Method 20 

Employing  Spheres  and  Cylinders  in  Skioscopy..  22 

Use  of  the  Ski-optometer  in  Subjective  Testing..  23 

A  Simplified  Subjective  Method 24 

Procedure  for  Using  Minus  Cyhnders 

Exclusively  26 

Constant  Attention  Not  Required 29 

Chapter  IV 

Important  Points  in  Connection  with  the  Use 

OF  THE  Ski-optometer 30 

Elimination  of  Trial  Frame  Discomfort 30 

Rigidity  of  Construction  31 

How  to  Place  the  Ski-optometer  in  Position 32 

Cleaning  the  Lenses 33 

Accuracy  Assured  in  Every  Test 34 

Built  to  Last  a  Lifetime 35 


CONTENTS— Continued 

Chapter  V  Page 

Condensed  Procedure  for  Making  Sphere  and 

Cylinder  Test  with  the  Ski-op tometer  37 

Subjective  Distance  Test 37 

Subjective  Reading  Test 40 

Chapter  VI 

Muscular  Imbalance 41 

The  Action  of  Prisms 42 

The   Phorometer 43 

The  Maddox  Rod 44 

Procedure  for  Making  the  Muscle  Test 45 

Binocular  and  Monocular  Test 47 

Chapter  VII 

The  Binocular  Muscle  Test 4S 

Made  with  the  Maddox  Rod  and  Phorometer...  48 

Esophoria  and  Exophoria 50 

Making  Muscle  Test  Before  and  After  Optical 

Correction  52 

When  to  Consider  Correction  of  Muscular  Im- 
balance    53 

Four  Methods  for  Correction  of  Muscular  Im- 
balance    54 

The  Rotary  Prism 54 

Use  of  the  Rotary  Prism  in  Binocular  Muscle 

Tests   56 

Chapter  VIII 

The  Monocular  Duction  Muscle  Test 58 

Made  with  Both  Rotary  Prisms 58 

Locating  the  Faulty  Muscle 58 

Adduction    59 

Abduction    61 


CONTENTS— Continued 

»  Page 

Superduction  62 

Subduction   63 

Procedure  for  Monocular  Muscle  Testing 64 

Diagnosing  a  Specific  Muscle  Case 65 

Chapter  IX 

First  Method  of  Treatment — Optical  Correc- 
tion    70 

Esophoria  70 

Treatment  for  Correcting  Esophoria  in  Children  72 
How  Optical  Correction  Tends  to  Decrease  6° 

Esophoria  in  a  Child 74 

Chapter  X 

Second    Method    of    Treatment  —  Muscular 

Exercise  75 

Made  with  Two  Rotary  Prisms  and  Red  Mad- 

dox  Rod 75 

Exophoria  75 

An  Assumed  Case  78 

Effect  of  Muscular  Exercise 80 

Home  Treatment  for  Muscular  Exercise  — 
Square  Prism  Set  Used  in  Conjunction 
with  the  Ski-optometer 82 

Chapter  XI 

Third  Method  of  Treatment — Prism  Lenses     84 

When  and  How  Employed 84 

Prism  Reduction  Method 85 

Chapter  XII 

A  Condensation  of  Previous  Chapters  on  the 
Procedure  for  Muscle  Testing  with 
the  Ski-optometer 87 


CONTENTS— Crw///////^^/ 

•  Page 

Four  Methods  of  Treating  an  Imbalance  Case 

when  the  Preceding  One  Fails 90 

Prisms   92 

Cyclophoria  92 

Chapter  XIII 

Cyclophoria  93 

Made  with  Maddox  Rods  and  Rotary  Prisms....  93 

Chapter  XIV 

Cycloduciton  Test 99 

Made  with  the  Combined  Use  of  the  Two  Mad- 
dox  Rods 99 

Treatment  for  Cyclophoria 102 

Chapter  XV 

Movements  of  the  Eyeballs  and  their  Ano- 
malies    105 

Monocular    Fixation 105 

Binocular  Fixation 106 

Orthophoria  ..•  107 

Heterophoria    107 

Squint    108 

Varieties  of  Heterophoria  and  Squint 109 

Chapter  XVI 

Law  of  Projection H-l- 

Suppression  of  Image 115 

Monocular  Diplopia  115 

Table  of   Diplopia 116 

Movement  of  Each  Eye  Singly 117 

Subsidiary  Actions 118 

Field  of  Action  of  Muscles 120 

Direction  of  the  Gaze 120 


CONTENTS— Co//./«./^^/ 

Page 

Primary  Position — Field  of  Fixation 121 

Binocular    Movements 121 

Parallel    Movements 122 

Lateral   Rotators 123 

Eye  Associates 124 

Movements  of  Convergence 125 

Movements  of  Divergence 125 

Vertical  Divergence 126 

Orthophoria  126 

Heterophoria  126 

Subdivisions  126 

Chapter  XVII 

Symptoms  of  Heterophoria 128 

Treatment    130 

Destrophoria   and   Laevophoria 132 


^  I  ''HE  demands  of  the  day  for  maximum 
efficiency  in  the  refracting  world  are 
largely  accountable  for  the  inception,  con- 
tinuous improvement  and  ultimate  develop- 
ment of  the  master  model  Ski-optometer. 

The  present  volume,  dealing  w^ith  the  in- 
strument's distinctive  operative  features,  has 
been  prepared  not  only  for  Ski-optometer 
users,  but  also  for  those  interested  in  the  sim- 
plification of  refraction  and  muscular  im- 
balance. 

The  author  is  indebted  for  invaluable 
counsel,  to 

Louis  J.  Ameno,  M.D.,  New  York. 
E.  LeRoy  Ryer,  O.D.,  New  York. 
Jos.  D.  Heitger,  M.D.,  Louisville,  Ky. 
W.  B.  Needles,  N.D.,  Kansas  City,  Mo. 


INTRODUCTORY 

1 X  7H1LE  in  a  measure  the  conventional  trial 
case  still  serves  its  purpose,  so  much  of  the 
refractionist's  time  is  consumed  through  the 
mechanical  process  of  individually  transfer- 
ring the  trial  case  spheres  and  cylinder  lenses, 
that  far  too  little  thought  is  given  to  muscular 
imbalance,  notwithstanding  its  importance  in 
all  refraction  cases. 

Dr.  Samuel  Theibold,  of  Johns  Hopkins 
University,  in  a  recent  address  before  the 
American  Medical  Association,  stated  that  the 
average  ref  ractionist  was  inclined  to  devote  an 
excess  of  time  to  general  refraction,  completely 
overlooking  the  important  test  and  correction 
of  muscular  imbalance.  If  the  latter  is  to  be 
at  all  considered,  general  refraction  must  be 
simplified — without  impairing  its  accuracy — 
a  result  that  is  greatly  facilitated  through  the 
use  of  the  Ski-optometer. 

One  must  admit  that  tediously  selecting  the 
required  trial-case  lens — whether  sphere,  cyl- 
inder or  prism — watching  the  stamped  num- 
ber on  the  handle — continual  wiping  and  in- 
serting each  individual  lens  in  a  trial  frame 
is  a  time-consuming  practise.  This  is  readily 
overcome,  however,  through  the  employment 
of  the  Ski-optometer. 


INTRODUCTORY 

In  a  word,  the  Ski-optomctcr  is  practically 
an  automatic  trial  case,  bearing  the  same  rela- 
tion to  the  refracting  room  as  the  accepted 
labor  and  time-saving  devices  of  the  day  bear 
to  the  commercial  world. 

The  present  volume  has  accordingly  been 
published,  not  alone  in  the  interest  of  those 
possessing  a  Ski-optometer,  but  also  for  those 
interested  in  attaining  the  highest  point  of  ef- 
ficiency in  the  work  of  refraction  and  muscu- 
lar imbalance. 


Ski-cptorneter  Lens  Battery 
[ahnost  actual  i/zf]  shoiv- 
ing  hoiv  sphere  and  cyl- 
inder lenses  are  procured. 


Supple  in  e  n  t  a  r  y  Disk 
Handle    and    Indicator. 


Cylinders 
Register  Here 


1st — Turn    this  Single  Reel  to  obtain  all   your 
spherical  lenses,  whether  convex  or  concave. 


2nd — Set  this  axis  indicator,  which  automat- 
ically positions  each  cylinder  lens  at  the  axis 
designated. 


3rd — Then  merely  turn  this  Single  Reel  to 
obtain  your  various  cylinder  lens  strengths  at 
that  axis. 


After  obtaining 
FINAL  results, 
your  prescription  is 
automatically  re- 
gistered, ALL 
READY  for  you 
to  transcribe. 


Fig.    1 — The    three    time-saving    moves    necessary   in    the 
operation    of   the    Ski-optometer. 


Chapter  I 
SKI-OPTOMETER  CONSTRUCTION 

A   FAR  better  understanding  of  the  instru- 
ment will  be  secured  if  the  refractionist 
possessing  a  Ski-optometer  will  place  it  before 
him,  working  out  each  operation  and  experi- 
ment step  by  step  in  its  proper  routine. 

The  three  moves  as  outlined  in  Fig.  1  should 
first  be  thoughtfully  studied  and  the  method  of 
obtaining  the  spheres  and  cylinders  carefully 
observed. 


Fig.  2— To  Obtain  Piano. 

1 — Set  spherical  indicator   at  "000"   as  illustrated    above. 

2 — Set  cylinder  indicator  to  "0". 

3 — Set  pointer  of  supplementary  disk   at  "open". 

The  instrument  should  then  be  set  at  zero  or 
''piano,"  a  position  indicated  by  the  appear- 


[1] 


Refraction    and   Muscular   Imbalance 

ance  of  the  three  ^'o  o  o''  at  the  spherical 
register,  in  conjunction  with  one  ^'o,"  or  zero, 
for  the  cylinder  at  its  register,  marked  ^'CC 
Cyl." 

After  this  move,  the  supplementary  disk's 
pointer  should  be  set  at  ''open"  (Fig.  2). 


sphere 
Ind'u  /itor 


Fig.    3 — To    obtain    sphericals,    turn    this    Single    Reel    as 

shown  by  dotted   finger.     This  assures   an   automatic   and 

simultaneous    registration    at    sphere    indicator    of    focus 

of  lens  appearing  at  sight  opening. 

Convex  Spherical  Lenses 

A  careful  study  will  show  that  the  Ski- 
optomoter's  spherical  lenses  are  obtained  by 
merely  turning  the  smaller  reel  (Fig.  3). 
The  first  outward  turn  of  this  reel,  toward  the 
temporal  side  of  the  instrument,  draws  into 
position  in  rcguhir  order  the  spherical  lenses 


[2] 


Refraction    and   Muscular   Imbalance 


-f.25,   +.50,   +.75,   and   +1.D.,   as   shown   in 
Fig.  3a. 


3-A  —  Outer       spherical 

reel      containing      Cx. 

sphericals    from    .025    to 

l.OOD   and    a  blank. 


3-B  —  Inner        spherical 

disk      containing      Cx. 

sphericals,  automatically 

turns  within   3-A. 


3-C  —  Supplementary 


spherical   disk. 

By  means  of  a  concealed  tooth  gear,  an  inner 
disk  is  automatically  picked  up,  placing  its 
first  lens  +1.25D  in  position  (Fig.  3b).  This 
+  1.25D  spherical  lens  remains  stationary 
while  the  outer  disk  again  revolves,  adding 
to  it  the  original  +.25,  +.50,  +.75  and  +1.D., 


[3] 


Refraction   and  Muscular   Imbalance 


Fig.  4 — With  the  reappearance  of  "00"  at  sphere  indicator, 

a  rapid  increase  or  decrease  of  +1.25  is  accurately  and 

speedily   attained, 

the  latter  totalling  +2.25D.  At  this  point,  the 
instrument  again  automatically  picks  up  its 
inner  disk,  thereby  placing  its  second  lens, 
+2. SOD,  in  position. 

Instead  of  using  intermediate  strengths  in 
making  an  examination,  it  is  frequently  desir- 
able to  make  such  extended  changes  as  1.2SD 
to  2. SOD.  With  the  Ski-optometer,  the  re- 
fractionist  will  note  that  two  white  zeros  ap- 
peared at  the  spherical  register  in  connection 
with  +1.2S,  and  again  with  +2. SO.  A  rapid 
outward  turn  of  the  spherical  reel  toward  the 
temporal  side  to  the  point  of  the  reappearance 
of  the  two  zeros  will  show  +3.7SD;  or,  if  in- 
creased power  is  still  desired,  a  rapid  turn  will 
draw +5. D.  into  position  (Fig.  4). 

[4] 


Refraction   and  Muscular  Imbalance 

Turning  the  reel  inward  toward  the  nasal 
side  will  likewise  decrease  its  convex  power. 
In  brief,  each  one  of  these  lenses,  showing 
their  foci  in  conjunction  with  the  two  white 
zeros,  are  signals  indicating  the  rapid  increase 
or  decrease  of  one  and  one-quarter  diopter. 
After  continuing  to  +6D.,  the  next  turn  auto- 
matically shows  zero  (or  ^'plano"),  the  origi- 
nal starting  point,  which  is  again  indicated  by 
the  three  white  zeros. 

Through  the  turn  of  the  single  reel — an  ex- 
clusive Ski-optometer  feature — all  convex 
spherical  lenses  have  now  been  attained  in 
quarters  up  to  -r6.D,  practically  covering 
ninety  percent  of  all  refraction  cases. 


Fig.    5 — With    supplementary    disk    pointer    set    at    -j-    6 

Sph.,   this  places   an    additional    +    6.D   spherical   lens    at 

sight      opening,      extending      instrument's      total      convex 

spherical  power  to  +12. D. 

[5] 


Refraction    and   Muscular   Imbalance 

Should  still  greater  power  be  desired,  the 
small  pointer  at  the  outer  edge  of  the  instru- 
ment should  be  set  at  +6  sphere  (Fig.  5). 
This  controls  a  supplementary  disk  (Fig.  3c) 
which  places  an  additional  +6D.  lens  before 
the  original  range  of  lenses  previously  referred 
to,  thus  increasing  the  maximum  power  to 
+  12D.  If  still  greater  strength  is  required, 
any  additional  trial  case  lens  may  be  added,  a 
cell  being  provided  for  that  purpose  on  the 
forward  plate  of  the  instrument. 

Operates  and  Indicates  Automatically 

As  previously  explained,  in  using  the  Ski- 
optometer,  it  is  only  necessary  to  remember 
that  each  outward  turn  of  the  single  reel 
toward  the  temporal  side  of  the  patient  in- 
creases the  plus  power,  while  the  reverse  turn 
toward  the  patient's  nose  decreases  it.  In  fact, 
no  attention  need  ever  be  given  the  register 
until  the  required  sum-total  is  secured,  it  only 
being  necessary  to  turn  the  single  reel  in  order 
to  be  assured  of  the  unvarying  and  accurate 
operation  of  the  instrument. 

For  convenience,  the  contour  or  upper  edge 
of  the  plate  covering  the  spherical  reel  has 
been  made  to  fit  the  index  finger  (Fig.  3). 
Hence  the  operator  should  note  that  it  requires 
but  one  complete  turn  from  extreme  side  to 


[6] 


Refraction    and   Muscular   Imbalance 

side,  rather  than  a  number  of  short  turns,  in 
order  to  bring  each  individual  lens  into  posi- 
tion, thus  obtaining  the  full  advantage  of  the 
automatic  spring-stop.  This  likewise  permits 
the  refractionist  to  operate  the  Ski-optometer 
even  though  the  room  is  in  total  darkness. 

Concave  Spherical  Lenses 

Another  simple  and  exclusive  Ski-optom- 
eter advantage  w^orthy  of  note  is  the  method 
employed  in  obtaining  concave,  spherical 
lenses.  Instead  of  employing  a  battery  of  con- 
cave lenses  similar  to  the  convex  battery  pre- 
viously described,  the  instrument's  operation 
is  greatly  simplified  through  the  use  of  a  neu- 
tralizing process. 

In  short,  the  Ski-optometer  only  contains 
two  concave  lenses  to  obtain  its  entire  series — 
namely,  a  — 6.D  and  a  — 12.D  sphere  (Fig. 
3c) — first  setting  the  pointer  of  the  sup- 
plementary disk  at — 6.  sphere,  then  setting  the 
indicator  of  the  spherical  battery  at  +6. 

Thus  zero  (or  piano)  is  obtained,  the  plus 
neutralizing  the  minus. 

By  merely  turning  the  plus  or  convex  spher- 
ical reel  inward,  or  toward  the  patient's  nose, 
the  convex  power  is  then  decreased,  naturally 
increasing  the  concave  value  or  total  minus 
lens  power.    For  example,  if  the  spherical  in- 


[7] 


Refraction    and   Muscular   Imbalance 


dicator  shows  +S.D,  when  the  — 6D.  lens  is 
placed  behind  it,  the  lens  value  at  the  sight 
opening  will  be  — ID  (Fig.  6).  If  re- 
quired, the  refractionist  may  continue  on  this 
plan  until  only  the  — 6D.  lens  remains. 


Fig.  6 — With  this  indicator  of  supplementary  disk,  set  at 
— 6.D,  Sph.  and  spherical  indicator  at  +5.0 — lens  value 
at  sight  opening  is  — l.D.  Sph.  This  simple  arrangement 
makes  it  possible  to  operate  the  Ski-optometer  with  but 
Single  Reel  for  both  plus   and   minus  sphericals. 

Should  concave  power  stronger  than  — 6D. 
be  desired,  by  placing  the  pointer  of  the  sup- 
plementary disk  at  — 12D.  Sph.  and  proceed- 
ing to  neutralize  as  before,  all  the  concave 
powers  up  to  — 12D.  in  quarters  are  similarly 
obtained.  For  the  convenience  of  the  opera- 
tor, all  minus  or  concave  spherical  powers  are 
indicated  in  red;  while  plus,  or  convex  pow- 
ers, are  indicated  in  white. 


[8] 


Refraction    and   Muscular   Imbalance 

The  instrument  is  also  provided  with  an 
opaque  or  blank  disk  which  is  brought  into 
position  before  the  sight  opening  by  setting 
the  pointer  of  the  supplementary  disk  at 
''shut"  (Fig.  3c.) 

Summing  up,  all  plus  and  minus  spherical 
powers  have  been  attained  from  zero  to  12D. 
in  quarters,  practically  through  the  turn  of  the 
smgle  reel — a  simplicity  of  operation  largely 
responsible  for  Ski-optometer  supremacy. 


[9] 


Chapter  11 

CYLINDRICAL  LENSES 

TT  is  commonly  admitted  that  setting  each 
trial  case  cylindrical  lens  at  a  common  axis 
is  the  most  tedious  part  of  refraction. 

The  automatic  cylinder,  one  of  the  Ski- 
optometer's  latest  and  distinctly  exclusive  fea- 
tures, not  only  overcomes  this  annoyance  but 
also  avoids  the  need  of  individually  trans- 
ferring each  cylindrical  lens  according  to  the 
varying  strengths. 


Fig.  7 — Once  you  set  the  axis  indicator  as  shown  by  ciotted 
finders,    each    cylindrical     lens    in    the    instrument     auto- 
matically   positions    itself    exactly    at    that    axis,    as    indi- 
cated  by  the   arrow. 

By  merely  setting  the  Ski-optometer's  axis 
indicator  (Fig.  7),  each  cylindrical  lens  in 
the  instrument  automatically  positions  itself, 


[10] 


Refraction    and   Muscular   Imbalance 

so  that  it  will  appear  at  the  opening  at  the 
exact  axis  indicated. 

This  is  readily  accomplished  by  placing  the 
thumb  on  the  small  knob,  or  handle  of  the 
axis  indicator,  drawing  it  outward  so  as  to 
release  it  from  spring  tension.  The  indicator 
may  then  be  set  at  any  desired  axis;  and,  on 
releasing  the  handle,  every  cylinder  in  the  in- 
strument becomes  locked,  making  it  impos- 
sible for  any  lens  to  appear  at  an  axis  other 
than  the  one  specified  by  the  indicator. 

This  insures  the  absolute  accuracy  of  the 
axis  of  every  cylinder  as  it  appears  before  the 
patient's  eye.  Subsequent  shifting  of  the  axis 
even  to  a  single  degree  is  impossible,  al- 
though it  is  a  common  occurrence  where  trial- 
case  lenses  are  employed. 

Obtaining  Correct  Focus 

After  setting  the  axis  indicator,  the  only  re- 
maining move  is  to  obtain  the  correct  cylin- 
drical strength  or  focus.  This  is  readily  ac- 
complished by  merely  turning  the  Ski-optom- 
eter's  larger  or  extreme  outer  single  reel, 
which  contains  concave  cylindrical  lenses 
from  .2SD  to  2D  in  quarters  (Fig.  8a).  It 
should  again  be  borne  in  mind  that  a  down- 
ward turn  increases  concave  cylinder  power, 
while  an  upward  turn  decreases  it.  The  oper- 

[11] 


Refraction   and  Muscular   Imbalance 

ation  of  the  cylinder  reel  is  greatly  facilitated 
by  carefully  noting  position  of  thumb  and  in- 
dex finger  (Fig.  8).  Thus  accuracy  of  result, 
simplicity  of  operation  and  the  saving  of  much 
valuable  time  is  invariably  assured. 


Fig.  8A — Inner  cog-wheel  construction,  showing  arrange- 
ment  of   Ski-optometer   cylinders.     This   simple   construc- 
tion   assures    accuracy    and     avoidance    of    the    slightest 
shifting  of  axes. 

As  each  cylinder  appears  before  the  pa- 
tient's eye,  it  simultaneously  registers  its  focus 
at  the  indicator  marked  "CC  CYL"  shown  in 
Fig.  8.  Examinations  of  greater  accuracy 
could  not  possibly  be  made  than  those  obtained 
through  the  Ski-optometer,  hence  no  refrac- 
tionist  should  hesitate  to  employ  it  throughout 
an  eni'ire  examination — wherever  trial-case 
lenses  are  used. 

The  range  of  the  Ski-optometer's  cylinder- 
lens  battery  includes  up  to  2D.  in  quarters. 
An  axis  scale  and  a  cell  is  located  at  the  back 


[12] 


Refraction   and  Muscular  Imbalance 


of  the  instrument  for  insertion  of  an  additional 
trial-case  cylinder  lens,  when  stronger  cylin- 


Fig.   8 — Turn  this  Single  Reel   as  shown  by  dotted   finger 

to  obtain  cylindrical  lenses,  which  simultaneously  register 

their  focus  as  they  appear.     Each  lens  also  automatically 

positions    itself    at    axis    designated. 

drical  power  is  required.  For  example,  if  an 
additional  — 2D.  cylinder  is  added,  it  will  in- 
crease the  range  up  to  4D.  cylinder;  or  if 
twelfths  are  desired,  an  0.12D.  cylinder  lens 
may  be  inserted.  In  this  connection,  it  is  in- 
teresting to  note  that  considerable  experiment- 
ing with  twelfths  in  the  Ski-optometer  proved 
them  to  be  needless,  inasmuch  as  the  instru- 
ment's cylindrical  lenses  set  directly  next  to 
the  patient's  eyes  overcome  all  possible  loss  of 
refraction,  as  explained  in  a  later  paragraph. 


[13] 


Refraction   and  Muscular  Imbalance 

Why  Concave  Cylinders  Are  Used  Exclusively 

The  Ski-optometer  contains  only  concave 
cylinders,  as  it  is  universally  admitted  that 
convex  cylinders  are  not  essential  for  testing 
purposes. 

In  fact,  concave  cylinders  should  alone  be 
used  in  making  an  examination,  even  where  a 
complete  trial-case  is  employed.  To  repeat 
one  of  the  first  rules  of  refraction:  "As  much 
plus  or  as  little  minus  spherical  power  as  pa- 
tients will  accept,  combined  with  weakest 
minus  cylinder,  simplifies  the  work  of  refrac- 
tion and  insures  accuracy  without  time- 
waste." 

After  an  examination  with  the  Ski-optom- 
eter is  completed,  the  total  result  of  plus 
sphere  and  minus  cylinder  may  be  transposed 
if  desired,  though  in  most  intances  it  is  pre- 
ferable to  prescribe  the  exact  findings  indi- 
cated by  the  instrument.  This  will  also  avoid 
every  possibility  of  error,  eliminating  respon- 
sibility where  one  is  not  familiar  with  trans- 
position— since,  after  all,  it  is  the  duty  of  the 
optician  to  thoroughly  understand  that  part 
of  the  work. 

Transposition  of  Lknses 

It  is  commonly  understood  that  transposi- 
tion of  lenses  is  merely  change  of  form,  but 
not  of  value. 

[14] 


Refraction   and  Muscular   Imbalance 

For  example,  a  lens  +1.00  sph.  =  — .50  cyl. 
axis  180°  may  be  transposed  to  its  equivalent, 
which  is  -r  .50  sph.  ==  4-  .50  cyl.  axis  90^ 
The  accepted  formula  in  this  special  instance 
is  as  follows :  Algebraically  add  the  two  quan- 
tities for  the  new  sphere,  retain  the  power  or 
the  original  cylinder,  but  change  its  sign  and 
reverse  its  axis  90  degrees.  Applying  this 
rule,  a  lens  -r  .75  sph.  =  —  .25  cyl.  axis  180°, 
is  equivalent  to  +  .50  sph.  =  +  .25  cvl.  axis 
90°. 

Similarly,  a  lens  +1.00  sph.  =  —  1.00  cyl. 
axis  180°  is  equivalent  to  +1.00  cyl.  axis  90°. 

One  of  the  difficulties  in  transposing  is  in 
reversing  the  axis.  In  such  cases,  it  is  well 
to  m_emorize  the  following  simple  rule : 

To  reverse  the  axis  of  any  cylindrical  lens 
containing  three  numerals — add  the  first  two 
together  and  carry  the  last.  For  example, 
from  105  to  180  degrees,  etc.: 

105°   Add — one  and  "0"  equals  1  Then  carry  the   5  =   15° 

120°   Add— one  and  two  equals  3  Then  carry  the  0  =  30° 

130°   Add — three  and  one  equals  4  Then  carry  the  0  =  40° 

150°   Add — live  and  one  equals  6  Then  carry  the  0  ^  60° 

165°   Add — six   and  one   equals   7  Then  carry  the   5  =  75° 

180°   Add — eight  and  one  equals  9  Then  carry  the  0  ^  90° 

To  transpose   where  there   are  but  tivo  numerals,  90°  should 
be  added. 

In  using  the  Ski-optometer,  it  is  absolutely 
unnecessary  to  transpose  the  final  result  of  an 
examination;  merely  write  the  prescription  as 


[15] 


Refraction   and   Muscular   Imbalance 


instrument  indicates.  The  idea  that  plus 
sphere  combined  with  minus  cylinder,  or  the 
reverse,  is  an  incorrect  method  of  writing  a 
prescription,  has  long  since  been  disproved. 


[16] 


Chapter  III 

HOW  THE  SKI-OPTOMETER  ASSISTS  IN 
REFRACTION 

^"T^HE  construction  of  the  Ski-optometer  has 
now  been  fully  explained,  and  the  reader 
realizes  that  since  the  instrument  contains  all 
the  lenses  necessary  in  making  an  examination, 
greater  operative  facility  is  afforded  through 
its  use  than  where  the  trial-case  lenses  are  em- 
ployed. 

The  Ski-optometer  is  ^'an  automatic  trial- 
case"  in  the  broadest  sense  of  the  term,  wholly 
superseding  the  conventional  trial-case.  It 
should  therefore  be  employed  throughout  an 
entire  examination,  wherever  trial-case  lenses 
were  formerly  used.  To  fully  realize  its 
labor  saving  value  in  obtaining  accurate  ex- 
amination results,  it  is  only  necessary  to  recall 
the  tedious  method  of  individually  handling 
and  transferring  each  lens  from  the  trial-case 
to  the  trial-frame,  watching  the  stamped  num- 
ber on  each  lens  handle,  wiping  each  lens  and 
in  the  case  of  cylindrical  lenses  setting  each 
one  at  a  designated  axis — all  being  needless 
steps  where  the  Ski-optometer  is  employed. 

The  Use  of  the  Ski-optometer  in  Skioscopy 
In  skioscopy,  the  Ski-optometer  offers  the 

refractionist  assistance  of  the  most  valuable 

character. 


[17] 


Refraction   and  Muscular  Imbalance 

For  example,  assuming  that  extreme  motion 
in  the  opposite  direction  with  plane  or  con- 
cave mirror  is  obtained  with  a  +1 .2SD.  spheri- 
cal lens  before  the  patient's  eye;  by  quickly 
turning  the  Ski-optometer's  single  reel  until 
the  two  white  zeros  again  appear,  +2. SOD  is 
secured,  as  explained  in  the  previous  chapter. 
If  this  continues  to  give  too  much  ''against 
motion,"  the  lens  power  should  be  quickly  in- 
creased to  +3.75  or  +S.OOD  if  necessary 
(Fig.  4) .  Should  the  latter  reveal  a  shadow  in 
the  reversed  direction,  the  refractionist  is  as- 
sured that  it  is  the  weakest  lens  that  will  cause 
its  neutralization.  Practically  but  few  lenses 
have  been  used  to  obtain  the  final  result  prov- 
ing the  instrument's  importance  and  time-sav- 
ing value  in  skioscopy,  and  demonstrating  the 
simplicity  with  which  tedious  transference  of 
trial-case  lenses  is  avoided. 

Furthermore,  it  should  be  noted  that  where 
the  Ski-optometer  is  used  in  skioscopy,  it  is 
not  necessary  to  remove  the  retinoscope  from 
the  eye  or  to  constantly  locate  a  new  reflex 
with  each  lens  change.  This  permits  a  direct 
comparison  of  the  final  lens  and  eliminates  the 
usual  difficulty  in  mastering  skioscopy.  The 
chief  cause  of  this  difficulty  is  due  to  the  fact 


[18] 


Refraction   and   Muscular   Imbalance 

that  the  transferring  of  the  trial-case  lenses 
makes  it  practically  impossible  for  the  student 
to  determine  whether  the  previous  lens  caused 
more  'Svith"  or  ''against"  motion. 

Where  the  indirect  method  is  employed  in 
skioscopy,  best  results  are  secured  through  the 
use  of  the  Woolf  ophthalmic  bracket  and  con- 


Fig.    9 — The   Woolf   ophthalmic   bracket.      A    convenient 

and   portable    accessory  in   skioscopy  and  muscle  testing; 

can  be  used  with  or  without  Greek  cross. 

centrated  filament  lamp, together  with  an  iris 
diaphragm  chimney.  The  latter  permits  the 
reduction  or  increase  of  the  amount  of  light 
entering  the  eye,  as  it  is  agreed  that  a  large 
pupil  requires  less  light,  a  small  pupil  re- 
quiring more  light.  The  bracket  referred  to 
permits  the  operator  to  swing  the  light  into 
any  desired  position  (Fig.  9),  while  the 
iris  diaphragm  chimney  serves  as  a  shutter. 
This   apparatus   may   also   be   employed    for 


[19] 


Refraction  and  Muscular  Imbalance 

muscle  testing,  as  described  in  a  subsequent 
paragraph. 

A  Simplified  Skioscopic  Method 
In  using  the  Ski-optometer,  instead  of 
working  forty  inches  away  from  the  patient 
in  skioscopy  and  deducting  I.D.,  the  refrac- 
tionist  will  find  it  more  convenient  to  work  at 
a  twenty-inch  distance,  deducting  2.D.  This 
working  distance  may  be  accurately  mea- 
sured and  maintained  by  using  the  reading 
rod  accompanying  the  instrument.  Instead 
of  deducting  2.D.  from  the  total  findings, 
however,  it  is  preferable  to  insert  a  +2.D. 
trial  case  lens  in  the  rear  cell  of  the  instru- 
ment directly  next  to  the  patient's  eye.  After 
determining  the  weakest  lens  required  to  neu- 
tralize the  shadow  in  both  meridians,  the  ad- 
ditional +2.D.  lens  should  be  removed  and 
the  total  result  of  the  examination  read  from 
the  instrument's  register. 

To  illustrate  a  case  in  skioscopy  where 
spherical  lenses  are  employed  to  correct  both 
meridians,  assume  that  the  vertical  shadow 
requires  a  +1.2SD  lens  to  cause  its  reversal, 
while  the  horizontal  recjuires  +2.00D.  Em- 
ployment of  the  customary  diagram,  illus- 
trated in  Fig.  10,  would  show  the  patient  re- 
quired M.2S  sph.  -~  +.75  cyl.  axis  90,  which 


[20] 


Refraction    and   Muscular   Imbalance 

when  transposed  is  equivalent  to  +2.00  Sph. 
=  —.75  cyl.  axis  180°. 


-I-  ZOO 


Fig.    10 — Where    spherical    lenses    are    employed    in    Ski- 
oscopy,  above  indicates  patient  requires 

-1-  125  Sph.  =  +  75  Cyl.  Axis  90° 
or  +  2  Sph.  =  —  75  Cyl.  Axis  180° 

It  should  be  noted  that  the  total  spherical 
power  is  +2.00D,  as  the  Ski-optometer's 
register  shows,  while  the  difference  between 
the  two  meridians  is  75,  which  is  the  required 
strength  of  the  cylinder.  By  then  turning  the 
cylinder  reel  to  .75,  and  setting  the  axis  indi- 
cator at  180°  (because  by  using  minus  cylin- 
ders, the  axis  must  be  reversed)  the  patient 
should  read  the  test  type  with  ease  if  the  ski- 
oscopic  findings  are  correct.  Thus  with  the 
Ski-optometer,  it  is  not  even  necessary  to  learn 
transposition,  since  the  instrument  automati- 
cally accomplishes  the  work,  avoiding  all  pos- 
sibility of  error. 


[21] 


Refraction    and   Muscular   I w balance 


Employing  Sphlrhs  and  Cylinders  in  Skioscopy 

Another  commonly  used  objective  method 
may  be  employed  with  even  greater  facility 
through  the  combined  use  of  both  the  Ski- 
optometer's  spherical  and  cylindrical  lenses. 
As  previously  suggested,  insert  the  +2.00 
spherical  trial-case  lens  in  the  rear  of  the  in- 
strument, working  at  a  twenty  inch  distance, 
then  proceed  to  correct  the  strongest  meridian 
first. 

It  was  assumed  that  it  required  a  +2.00 
spherical  to  neutralize  the  strongest,  or  hori- 
zontal meridian,  as  shown  in  Fig.  10.  The  re- 
fractionist  should  then  set  the  axis  indi- 
cator therewith,  which  is  the  axis  of  the  cylin- 
der, or  180°. 

It  is  then  merely  a  matter  of  increasing  the 
Ski-optometer's  cylindrical  lens  power  until 
the  reversal  of  the  shadow  in  the  weakest 
meridian  is  determined.  Assuming  this 
proves  to  be  — .75  cylinder,  axis  180°,  the 
patient's  complete  prescription  +2.00  sph.  = 
— .75  cyl.  axis  180°,  would  be  registered  in  the 
Ski-optometer  without  any  further  lens  change 
other  than  the  removal  of  the  +2.00  working 
distance  lens. 

However,  regardless  of  the  method  em- 
ployed, the   Ski-optometer   greatly   simplifies 


[22] 


Refraciion    and   Muscular   Imbalance 

skioscopy.  In  fact,  the  instrument  was  origi- 
nally intended  to  simplify  retinoscopy  or  skio- 
scopy, as  the  subject  should  be  termed,  the 
name  ''Ski-optometer"  having  been  derived 
from  the  latter. 

Use  of  the  Ski-optometer  in  Subjective  Testing 

In  subjective  refraction,  especially  where 
the  "better  or  worse"  query  must  be  decided 
by  the  patient,  it  is  commonly  understood  that 
the  refractionist  is  compelled  to  first  increase 
and  then  decrease  a  quarter  of  a  diopter  before 
the  final  lens  is  decided.  With  the  Ski-opto- 
meter, the  usual  three  final  changes  are  made 
in  far  less  time  than  it  takes  to  make  even  one 
lens  change  from  trial-case  to  trial-frame. 

For  example : 

Assuming,  with  a  +1.2SD  spherical  lens 
before  the  patient's  right  eye,  he  remarks  that 
he  "sees  better"  with  a  +1.D.  while  +.75D  is 
not  as  satisfactory.  The  refractionist  can  then 
quickly  return  to  +1.D.,  simply  turning  the 
Ski-optometer's  single  reel  outward  to  in- 
crease, or  backward  to  decrease,  the  lens 
strength.  So  rapidly  have  these  lens  changes 
been  made,  that  the  patient  quickly  sees  the 
difTference  of  even  a  quarter  diopter,  and 
quickly  replies,  "better"  or  "worse." 

This  is  made  possible  because  the  eye  does 


[23] 


Refraction    and    Muscular    Imbalance 

not  ''accommodate"  as  quickly  as  the  lens 
change  made  with  the  Ski-optometer.  It 
should  also  be  noted  that  the  eye  receives  an 
image  on  its  retina  within  one-sixteenth  of  a 
second;  otherwise,  the  patient  is  forced  to  ac- 
commodate, making  it  difficult  to  see  the  dif- 
ference of  even  a  quarter  dioptre.  On  the 
other  hand,  in  transferring  trial-case  lenses, 
with  its  slow,  tedious  procedure,  the  patient, 
being  unable  to  detect  the  slight  difference  of 
only  a  quarter  diopter,  unhesitatingly  replies, 
*^no  difference,"  merely  because  they  are  com- 
pelled to  accommodate. 

A  Simplified  Subjective  Method 

The  following  simplified  method  of  pro- 
cedure is  suggested  for  subjective  testing  with 
the  Ski-optometer,  although  as  previously  ex- 
plained, the  refractionist  may  employ  his  cus- 
tomary method,  overcoming  the  annoyance  of 
transferring  trial-case  lenses  and  the  setting  of 
each  cylinder  individually.  The  Ski-optom- 
eter has  been  constructed  and  based  upon  the 
golden  rule  of  refraction :  ''As  much  plus  or 
as  little  minus  spherical,  combined  with  as 
little  minus  cylinder  power  as  the  patient 
accepts." 

By  applying  this  rule  as  in  the  above  method 
and  starting  with  +5.D.  spherical,  watching 


[24] 


Refraction    and   Muscular   Imbalance 


the  two  zeros  (Fig.  4)  and  rapidly  reduc- 
ing +  1.25D  each  time,  we  will  assume  that 
+  1.25D  gives  20/30  vision;  as  a  final  result 
+  1.D.  will  possibly  give  20/25  vision. 

The  patient's  attention  should  next  be  di- 
rected to  the  most  visible  line  of  type,  pre- 
ferably concentrating  on  the  letter  ''E"  or  the 
clock  dial  chart^ — either  of  which  will  assist  in 
determining  any  possible  astigmatism.  Since 
the  Ski-optometer  contains  concave  cylinders 
exclusively,  the  next  move  should  be  the  set- 
ting of  its  axis  indicator  at  180°,  commonly 
understood  as  "with  the  rule."  One  should 
then  proceed  to  determine  the  cylinder  lens- 
strength  by  turning  the  reel  containing  the 
cylindrical  lenses  (Fig.  8).  Should  the  pa- 
tient's vision  fail  to  improve  after  the  — .50D. 
cylinder  axis  180°  has  been  employed,  the  re- 
fractionist,  in  seeking  an  improvement,  should 
then  slowly  move  the  axis  indicator  through 
its  entire  arc. 

With  the  cylinder  added,  regardless  of 
axis,  poor  vision  might  indicate  the  absence 
of  astigmatism.  If  astigmatism  exists,  vision 
will  usually  show  signs  of  improvement 
at  some  point,  indicating  the  approximate 
axis.  Once  the  latter  is  ascertained,  the  re- 
fractionist  may  readily  turn  the  Ski-optom- 
eter's  cylinder  reel  and  obtain  the  correct  cyl- 

[25] 


Refraction    and   Muscular    Imbalance 


inder  lens  strength,  after  which  the  axis  in- 
dicator should  be  moved  in  either  direction  in 
order  to  obtain  the  best  possible  vision  for  the 
patient. 

The  refractionist  should  always  aim  to  ob- 
tain normal  (or  20/20)  vision  with  the  weak- 
est concave  cylinder,  combined  with  the 
strongest  plus  sphere,  or  weakest  minus  sphere. 

Procedure  for  Using  Minus  Cylinders 
Exclusively 

For  the  benefit  of  those  who  have  never  used 
minus  cylinders  exclusively  in  making  their 
examinations,  we  will  assume  that  the  patient 
requires  O.U.  fl.D  Sph.  =  — ID  cyl.  axis 
180°  for  final  correction;  the  latter,  in  its  trans- 
posed form,  being  equivalent  to  +1.D.  cylin- 
der axis  90°.  Unquestionably  the  best  method 
is  the  one  that  requires  the  least  number  of 
lens  changes  to  secure  the  final  result. 

To  obtain  this,  the  following  order  of  lens 
change  should  be  made:  First,  +r.D.  sphere 
is  finally  determined  and  allowed  to  remain  in 
place.  Concave  cylinders  are  then  employed 
in  quarters  until  the  final  results  of  +1.D. 
spherical,  combined  with  — l.D.  cylinder  axis 
180°  is  secured.  This  necessitates  the  change 
of  but  four  cylindrical  lenses  as  shown  in  rou- 
tine ''A"  as  follows: 


[26] 


Refraction    and   Muscular   Imbalance 

ROUTINE   "A"  ROUTINE   "B" 

(Made  with  minus  cylinder)  (Made  with  plus  cylinder) 

Sph.  +1.D.           Cvl.       Axis  Sph.  +1.D.  Cyl.       Axis 

Step   1  +1.D.  —  —25   ax.   180°  equal  to  +.75  =  +.25   ax.  90° 

Step  2  +1.D.  =  —50   ax.   180°  equal  to  +.50  =  +.50   ax.  90° 

Step  3  +1.D.  =  —75   ax.   180°  equal  to  +.25  =  +.75   ax.  90° 

Step  4  +1.D.  =  —1      ax.   180°  equal  to          0  +1     ax.  90' 

In  brief  the  method  of  using  minus  cylin- 
ders exclusively  in  an  examination,  as  ex- 
plained in  routine  ''A",  necessitates  the  change 
of  the  cylinder  lenses  only  after  the  strongest 
plus  sphere  is  secured. 

On  the  other  hand,  notwithstanding  in- 
numerable other  methods  where  plus  cylin- 
ders are  used,  routine  "B''  shows  that  the  best 
spherical  lens  strength  the  patient  will  accept, 
is  also  first  determined.  Then  both  spheres 
and  cylinders  are  changed  in  their  regular 
order  by  gradually  building  up  in  routine,  by 
increasing  plus  cylinder  and  next  decreasing 
sphere,  a  quarter  dioptre  each  time,  until  the 
final  result  is  secured. 

While  it  is  conceded  that  both  routine  "A" 
and  "B"  are  of  themselves  simplified  meth- 
ods, by  comparing  routine  ^^A"  where  minus 
cylinders  are  used  with  routine  ^'B"  where 
plus  cylinders  are  used  in  their  corresponding 
steps,  the  ref  ractionist  will  note  by  comparison 
that  one  is  the  exact  equivalent  and  transposi- 
tion of  the  other.     Where  plus  cylinders  are 


[27] 


Refraction    and   Muscular    Imbalance 

employed,  eight  lens  changes  are  made  be- 
fore final  results  are  secured;  while  but  four 
lens  changes  are  necessary  where  minus  cylin- 
ders are  used. 

The  refractionist  should  also  note  by  com- 
parison that  the  use  of  minus  cylinders  re- 
duces focus  of  the  plus  sphere,  but  only  in  the 
meridian  of  the  axis.  It  has  not  made  the  pa- 
tient myopic.  Furthermore,  a  plus  cylinder 
will  bring  the  focal  rays  forward,  while  minus 
cylinders  throw  them  backward  toward  the 
retina. 

This  is  but  another  reason  for  the  exclusive 
use  of  minus  cylinders  in  refraction. 

The  method  of  using  minus  cylinders  exclu- 
sively in  an  examination,  necessitates  the 
change  of  the  cylinder  lenses  only.  On  the 
other  hand,  the  method  of  using  plus  cylinders 
makes  it  necessary  to  change  spheres  and  cyl- 
inders in  routine. 

In  brief,  since  using  the  minus  cylinder  is 
merely  a  matter  of  mathematical  optics,  their 
use  even  in  a  trial-case  examination  is  strongly 
urged. 

The  maximum  value  of  the  Ski-optometer 
is  fully  realized  only  when  the  advantages  of 
using  minus  cylinders  exclusively  in  every  ex- 
amination is  clearly  understood. 


[28] 


Refraction    and   Muscular   Imbalance 

Constant  Attention  Not  Required 

With  the  Ski-optometer,  when  the  examina- 
tion is  completed,  the  sum-total  of  final  re- 
sults— whether  spherical,  cylinder,  axis,  or  all 
combined— are  automatically  indicated  or 
registered  ready  to  write  the  prescription. 
Until  then,  the  foci  of  the  various  lenses  that 
may  be  employed  are  of  no  importance. 

In  short,  in  using  the  Ski-optometer,  it  is 
not  necessary  to  constantly  watch  the  registra- 
tions during  examinations.  The  automatic 
operation  of  the  instrument  is  an  exclusive  fea- 
ture, so  that  the  refractionist  should  unhesi- 
tatingly employ  it.  Hence,  by  eliminating  the 
perpetual  watch  on  the  lenses  in  use,  the  re- 
fractionist is  enabled  to  give  his  undivided  at- 
tention to  the  patient  rather  than  to  the  trial 
lenses. 

Where  a  special  dark-room  is  used  for  ski- 
oscopic  work,  an  additional  wall  bracket  or 
floor-stand  will  necessitate  only  the  removal  of 
the  instrument  itself.  This  enables  the  refrac- 
tionist to  use  the  Ski-optometer  for  subjective 
or  objective  work,  without  disturbing  the  pa- 
tient's correction. 


[29] 


Chapter  IV 

IMPORTANT  POINTS  IN  CONNECTION 

WITH  THE  USE  OF  THE 

SKI-OPTOMETER 

^T^HE  Ski-optometer  is  equipped  with  an 
adjustable  head-rest,  permitting  its  lenses 
to  be  brought  as  close  as  possible  to  the  eye 
without  touching  the  patients  lashes,  a  matter 
of  importance  in  every  examination. 


in- 


Fig.    11 — The    nasal    lines    of    the    Ski-optqmeter    fit    the 
contour    of    face    with    mask-like    perfection,    patient    re- 
maining   in    comfortable    position. 


Elimination   of  Trial   Frami:   Discomfort 

Where  the  Ski-optometer  is  correctly  fitted 
to  the  face,  the  patient  invariably  remains  in 
a  comfortable  position  (Fig.  11).  The  in- 
strument is  shaped  to  fit  the  face  like  a  mask, 


[30] 


Refractioti    and   Muscular   Imbalance 

so  that  even  with  a  pupillary  distance  of  but 
SO  m/m  (that  of  a  child)  there  still  remains, 
without  pinching,  ample  room  for  the  widest 
nose  of  an  adult. 

Before  making  an  examination,  the  correct 
pupillary  distance  should  always  be  obtained 
by  drawing  an  imaginary  vertical  line  down- 
ward through  the  center  of  each  eye  from  the 
90°  point  on  the  Ski-optometer  axis  scale.  The 
pupillary  distance  will  then  register  in  milli- 
meters on  the  scale  of  measurements  for  each 
eye  separately.  If  the  Ski-optometer  is  cor- 
rectly adjusted,  the  patient  is  securely  held  in 
position,  the  cumbersome  trial-frame  being 
entirely  eliminated. 

Rigidity  of  Construction 

Illustration  on  following  page  (Fig.  11a) 
shows  the  reinforced  double  bearing  arms 
which  hold  the  Ski-optometer  lens  batteries  at 
two  points.  This  eliminates  possibility  of  the 
instrument  getting  out  of  alignment,  and  pre- 
vents wabbling  or  loose  working  parts. 

The  broad  horizontal  slides  shown  in  the 
cut,  move  in  and  out  independently  so  that 
the  pupillary  distance  is  obtained  for  each  eye 
separately  by  turning  the  pinioned  handle  on 
either  side  of  the  instrument.  The  scale  de- 
notes in  millimeters  the  P.D.  from  the  median 


[31] 


Refraction    and   Muscular   Imbalance 

line  of  the  nose  outward,   the  total  of  both 
scales  being  the  patient's  pupillary  distance. 
Fig.  1 1  a  also  serves  to  show  the  staunch  con- 
struction of  the  base  of  the  Ski-optometer. 


Handles  Controlling 

Pupillary  Distance 

for  Each  Eye  Separately 


Fig.  11 A — Showing  staunch  construction  of  Ski-optometer. 
base. 

How  TO  Place  the  Ski-optometer  in  Position 

The  patient  should  be  placed  in  a  comfort- 
able position  with  "chin  up,"  as  though  look- 
ing at  a  distant  object.  The  instrument  should 
then  be  raised  or  lowered  by  the  adjustable 
ratchet  wheel  of  the  bracket.  The  wall 
bracket  gives  best  results  when  suspended 
from  the  wall,  back  of  the  patient,  as  shown 
on  page  135.  This  bracket  should  be  placed 
about  ten  inches  above  the  head  of  the  aver- 


[32] 


Refraction    and   Muscular   Imbalance 

age  patient.  When  the  Ski-optometer  is 
placed  in  position  for  use,  its  lower  edge  will 
barely  touch  the  patient's  cheeks.  It  is  some- 
times advisable  to  request  the  patient  to  light- 
ly press  toward  the  face  the  horizontal  bar 
supporting  the  instrument.  Particularly 
good  results  are  secured  where  a  chair  with 
a  head-rest  is  employed  in  conjunction  with 
the  Ski-optometer.  (See  illustration  of  Model 
Refraction  Room,  Page  112). 

Cleaning  the  Lenses 

The  time-waste  of  perpetually  cleaning 
lenses  is  overcome  where  the  Ski-optometer  is 
employed.  For  the  convenience  of  the  opera- 
tor and  protection  of  Ski-optometer  lenses, 
the  latter  are  concealed  in  a  dust-proof  cell, 
overcoming  all  dust  and  finger-print  annoy- 
ances. When  not  in  use,  the  instrument  should 
be  covered  with  the  standardized  hood  form- 
ing part  of  the  equipment. 

The  instrument  should  not  be  taken  apart 
under  any  circumstances.  To  clean  its  lenses, 
not  a  single  screw  need  be  removed,  as  the  lens- 
es of  each  disk  may  be  cleaned  individually 
through  the  opening  of  the  other  disks.  These 
openings  are  conveniently  indicated  by  the 
white  zeros  (Fig.  2).  The  Ski-optometer 
contains  but  eleven  spherical  and  eight  cylin- 


[33] 


Refraction    and   Muscular   Imbalance 

drical  lenses  on  each  side,  so  that  the  actual 
work  of  cleaning  should  not  require  over  ten 
minutes  at  the  most,  cleaning  the  lenses  every 
other  week  proving  quite  sufficient. 

Accuracy  Assured  in  Every  Test 

Loss  of  refraction  is  completely  eliminated 
through  the  use  of  the  Ski-optometer.  The 
most  casual  examination  of  the  trial-frame  or 
any  other  instrument  shows  that  the  construc- 
tion necessitates  the  placing  of  the  spherical 
lens  next  to  the  eye  with  the  cylinder  lens  out- 
ermost— a  serious  fault  wholly  overcome  in 
the  Ski-optometer. 

Not  only  do  the  cylindrical  lenses  of  the 
Ski-optometer  set  directly  next  to  the  patient's 
eye,  thus  overcoming  any  possible  loss  of  re- 
fraction, but  the  strong  spherical  lenses  of  the 
supplementary  disk  are  set  directly  next  to  the 
cylinder.  There  is  apparently  but  a  hair's 
distance  between  these  lenses;  the  two  disks 
containing  the  spherical  lenses  of  the  Ski-op- 
tometer likewise  setting  close  together. 

In  a  word,  the  Ski-optometer's  cylinder 
lenses  set  directly  next  to  the  patient's  eye,  fol- 
lowed by  the  stronger  sphericals,  so  that  the 
weakest  spherical  or  +.25  (the  lens  of  least 
importance)  sets  farthest  away.  This  is  3i/< 
m/m   closer   than   any   trial   frame   manufac- 


[34] 


Refraction    and   Muscular   Imbalance 

tured,  however,  and  at  least  10  m/m  closer 
than  any  other  instrument — another  reason  for 
implicitly  relying  on  the  Ski-optometer  for 
uniformly  accurate  results. 

Built  to  Last  a  Lifetime 

The  Ski-optometer  is  built  on  the  plan  of 
1/lOOC,  insuring  absolute  rigidity  and  accu- 


Fig.  12— (A.  and  B.)— This  unique,  patented  split-spring 

device  of  screwless  construction,  securely  holds  all  movable 

parts.     In  case  of  repair,  they  may  be  removed  with  the 

blade  of  a  knife. 

racy  and  a  lifetime  of  endurance.  Particular 
and  detailed  attention  has  been  given  to  the 
novel  means  of  eliminating  screw^s  vs^hich 
either  bind,  create  friction  or  continually 
w^ork  loose,  causing  false  indications  of  find- 
ings on  scales  of  measurements;  hence  correct 
and   accurate   indications  are   insured   in  the 


[35] 


Refraction    and   Muscular   Imbalance 

Ski-optometer  by  means  of  a  split  spring- 
washer  construction  similar  to  that  of  an  auto> 
mobile  tire's  detachable  rim  (Fig.  12). 

This  patented  spring-washer  construction 
securely  holds  the  phorometer  lenses,  the  ro- 
tary prism  and  the  revolving  cylinder  lens 
cells. 

Whenever  necessary,  or  in  case  of  repair, 
these  parts  may  be  readily  removed  with  the 
blade  of  a  knife. 


[36] 


Chapter  V 

CONDENSED  PROCEDURE  FOR  MAKING 

SPHERE  AND  CYLINDER  TEST 

WITH  THE  SKI-OPTOMETER 

^J^OTWITHSTANDING  various  meth- 
ods employed,  for  both  subjective  and 
objective  refraction,  the  following  synopsis  of 
the  previous  chapters  will  unquestionably 
prove  most  valuable  to  the  busy  refractionist, 
enabling  him  to  make  error-proof  examina- 
tions in  practically  every  case  without  resort- 
ing to  the  transference  of  trial  case  sphere 
or  cylinder  lenses.  A  careful  reading  of 
chapters  one  and  two  should  be  made  how- 
ever, so  that  one  may  gain  an  understanding 
as  to  how  spheres  and  cylinders  are  obtained 
with  the  Ski-optometer. 

Subjective  Distance  Test 

1st — Place  Ski-optometer  in  position,  em- 
ploying spirit  level,  thus  maintaining  instru- 
ment's horizontal  balance. 

2nd — Adjust  the  pupillary  distance  for  each 
eye  individually,  by  drawing  an  imaginary 
vertical  line  downward  through  the  center  of 
each  eye  from  the  90°  point  on  the  Ski-optom- 
eter's  axis  scale.  The  opaque  disk  should  be 
placed  before  the  patient's  left  eye  by  setting 
the  supplementary  disk  handle  at  ''shut." 


[37] 


Refraction    and   Muscular   Imbalance 

3rd — The  Ski-optometer  lens  battery  before 
the  patient's  right  eye  should  be  set  at  "open" 
(figure  2),  whereupon  the  first  turn  of  spher- 
ical lens  battery  toward  the  nasal  side  places 
a  +6.D  sphere  in  position.  This  should  blur 
vision  of  average  patient. 

4th — It  is  now  only  necessary  to  remember 
that  an  outward  turn  toward  temporal  side  of 
the  instrument  increases  plus  sphere  power, 
while  a  nasal  turn  decreases  it.  Therefore  con- 
rnue  to  reduce  convex  spherical  lens  power 
until  the  large  letter  ''E"  on  the  distant  test 
card  is  clear.  Then  request  patient  to  read  as 
far  down  as  possible, — a  rapid  turn  of  a 
quarter  dioptre  being  readily  accomplished 
with  the  Ski-optometer  (Fig.  4). 

5th — In  the  event  of  working  down  to 
"zero"  with  spheres,  the  supplementary  disk 
handle  or  indicator  should  next  be  set  at  — 6.D 
sphere,  while  the  spherical  reel  should  be 
turned  toward  the  nasal  side — thus  building 
up  on  minus  spheres  (Fig.  6).  In  short, 
the  strongest  plus  sphere  or  weakest  minus 
sphere  should  always  be  determined  before 
employing  cylinders. 

6th — With  the  best  spherical  lens  that  the 
patient  will  accept  left  in  place,  direct  at- 
tention to  the  letter  E  or  F  in  the  lowest  line 
of  type  the  patient  can  see  on  the  distant  test 

[38] 


Refraction    and  Muscular   Imbalance 

letter  chart.  Then  set  axis  indicator  at  180° 
(Fig.  7). 

7th — Next  increase  concave  cylinder  power 
until  vision  is  improved.  If  vision  is  not  im- 
proved after  increasing  cylinder  strength  to 
— .50  axis  180°,  merely  reverse  the  axis  to  90°. 
If  vision  is  improved,  cylinder  lens  strength 
should  be  increased.  If  not,  it  should  be  de- 
creased  (Fig.  8). 

8th — Slowly  move  axis  indicator  through 
entire  arc  of  axis,  thus  locating  best  possible 
axis  (Fig.  7). 

9th — After  sphere  and  cylinder  test  of  right 
eye  has  been  made,  place  supplementary  disk 
handle  at  "shut."  Then  repeat  procedure  in 
testing  left  eye. 

10th — After  completing  examination  for 
each  eye  separately,  then,  with  both  of  the 
patient's  eyes  open,  direct  attention  to  lowest 
line  of  type  he  can  see,  concentrating  on  the  E 
or  F,  simultaneously  increasing  or  decreasing 
spherical  power  before  both  eyes.  The  re- 
fractionist  merely  recalls  that  by  turning  the 
Ski-optometer's  single  reel  toward  the  tem- 
poral side,  convex  spherical  power  is  in- 
creased, by  turning  toward  the  nasal  side  for 
either  eye,  spherical  power  is  decreased.  Cyl- 
inder lens  strength  may  be  changed  in  a  like 
manner  before  both  eyes  simultaneously. 

[39] 


Refraction    and   Muscular   Imbalance 

Uth — After  making  the  distance  test,  then 
only  is  it  necessary  to  copy  the  result  of  the 
examination  as  recorded  by  the  Ski-optom- 

eter. 

Subjective  Reading  Test 

Tilt  Ski-optometer  forward  in  making  read- 
ing test.  The  wide  groove  in  the  horizontal 
bar  supporting  the  instrument,  permits  it  to  be 
slightly  tilted. 

12th — Place  Ski-optometer  reading  rod  in 
position  with  card  at  about  14  inches.  Close 
off  one  eye.  Direct  patient's  attention  to  the 
name  ^'Benjamin"  printed  at  top  of  card. 

13th — Leave  cylinder  lens  in  place.  Pro- 
ceed as  in  distance  test  with  +6.D  sphere,  fog- 
ging down  until  the  first  word  ''laugh"  on  the 
reading  card,  in  line  75M,  is  perfectly  clear, 
this  being  slightly  smaller  than  the  average 
newspaper  type. 

14th — After  completion  of  examination 
for  each  eye  separately,  then  with  both  eyes 
direct  patient's  attention  to  word  "laugh." 
Move  reading  card  in  or  out  a  few  inches 
either  side  of  14  inch  mark.  This  will  de- 
termine any  possibility  of  an  over-correction. 
Then  record  prescription  just  as  Ski-optom- 
eter indicates.  For  a  detailed  description  of 
above,  as  well  as  for  objective  testing  with  the 
Ski-optometer,  read  chapter  three. 

[40] 


T 


Chapter  VI 

MUSCULAR  IMBALANCE 

'HE  purpose  of  the  present  chapter  is  to 
acquaint  the  refractionist  with  the  opera- 
tion of  the  Ski-optometer  as  "a  scientific  in- 
strument for  muscle  testing" — the  subject 
being  treated  as  briefly  and  comprehensively 
as  is  practicable. 

As  the  reader  progresses  in  the  subject  of 
muscular  anomalies,  he  may  carry  his  work 
to  as  high  a  plane  as  desired,  increasing  his 
professional  usefulness  to  an  enviable  degree. 

Through  the  use  of  the  Ski-optometer, 
muscle  testing  may  be  accurately  accom- 
plished in  less  time  than  a  description  of  the 
operation  requires.  Furthermore,  tedious  ex- 
aminations may  be  wholly  overcome  through 
the  discontinuance  of  the  consecutive  trans- 
ference of  the  various  degrees  of  prisms  from 
the  trial  case.  In  fact,  the  latter  method  has 
long  been  quite  obsolete,  owing  to  the  possi- 
bility of  inaccuracy.  The  muscle  action  of  the 
eye  is  usually  quicker  than  the  result  sought 
through  the  use  of  trial-case  prisms;  hence 
muscle  testing  with  the  Ski-optometer  is  ac- 
complished with  far  greater  rapidity  and  ac- 
curacy, thus  making  the  instrument  an  invalu- 
able appliance  in  every  examination. 


[41] 


Refraction    and   Muscular   Imbalance 

The  Action  of  Prisms 

Students  in  refraction — and  one  may  still  be 
a  student  after  years  of  refracting — are  some- 
times puzzled  as  to  just  what  a  prism  does 
when  placed  before  an  eye.  They  refer  to 
every  available  volume  and  are  often  confused 
between  ductions  and  phorias,  finally  drop- 
ping the  subject  as  an  unsolvable  problem.  In 
view  of  this  fact,  it  is  suggested  that  the  ref rac- 
tionist  should  read  the  present  volume  with 
the  actual  instrument  before  him. 

Before  proceeding,  one  should  first  under- 
stand the  effect  of  a  prism  and  what  it  ac- 
complishes. To  determine  this,  close  one  eye, 
looking  at  some  small,  fixed  object;  at  the 
same  time,  hold  a  ten-degree  prism  base-in 
before  the  open  eye,  noting  displacement  of 
the  object.  This  will  clearly  show  that  the 
eye  behind  the  prism  turns  toward  the  prism 
apex. 

To  carry  the  experiment  further,  the  fol- 
lowing test  may  be  employed  on  a  patient. 
Covering  one  eye,  direct  his  attention  to  a 
fixed  object,  placing  the  ten  degree  prism  be- 
fore the  eye,  but  far  enough  away  to  see  the 
patient's  eye  behind  it.  As  the  prism  is 
brought  in  to  the  line  of  vision,  it  will  be  seen 
that  the  eye  turns  towards  the   apex  of  the 


[42] 


Refraction   and  Muscular  Imbalance 

prism.     When  the  prism  is  removed,  the  eye 
returns  to  its  normal  position. 

Similar  experiments  enable  the  refraction- 
ist  to  make  the  most  practical  use  of  treating 
phorias  and  ductions,  as  well  as  to  compre- 
hend all  other  technical  work. 


Fig.  13 — An  important  part  of  the  equipment  for  muscular 
work. 

The  Phorometer 

As  previously  stated,  it  is  practically  impos- 
sible to  accurately  diagnose  a  case  of  muscular 
imbalance  with  trial  case  prisms.  For  this 
reason  the  phorometer  forms  an  important 
part  of  the  equipment  for  muscle  testing  in  the 
Ski-optometer,  having  proven  both  rapid  and 


[43] 


Refraction    and  Muscular  Imbalance 

accurate.  It  consists  of  two  five-degree  prisms 
with  bases  opposite,  each  reflecting  an  object 
toward  the  apex  or  thin  edge.  The  patient 
whose  attention  is  directed  to  the  usual 
muscle-testing  spot  of  light,  will  see  two  spots. 

Aside  from  the  instrument  itself,  and  in 
further  explanation  of  the  phorometer's  prin- 
ciple and  construction,  when  two  five-degree 
prisms  are  placed  together  so  that  their  bases 
are  directly  opposite,  they  naturally  neutral- 
ize; when  their  bases  are  together,  their 
strength  is  doubled.  Thus  while  the  prisms  of 
the  phorometer  are  rotating,  they  give  prism 
values  from  piano  to  ten  degrees,  the  same  be- 
ing indicated  by  the  pointer  on  the  phoro- 
meter's  scale  of  measurments. 

As  a  guide  in  dark-room  testing,  it  should 
be  noted  that  the  handle  of  the  phorometer 
in  a  vertical  position  is  an  indication  that  the 
vertical  muscles  are  being  tested;  if  hori- 
zontal, the  horizontal  muscles  are  undergoing 
the  test. 

The  Maddox  Rod 
The  Maddox  rod  (Fig.  14)  consists  of 
a  number  of  red  or  white  rods,  which  cause 
a  corresponding  colored  streak  to  be  seen 
by  the  patient.  This  rod  is  placed  most 
conveniently   on   the    instrument,   being   pro- 


[44] 


Refraction   and  Muscular  Imbalance 

vided  with  independent  stops  for  accurately 
setting  the  rods  at  90  or  180  degree  positions. 


Fig.  1-1 — The  Maddox  Rod,  a  valuable  aid  in  making 
muscular  tests. 

The  Maddox  rod  has  proven  of  valuable  as- 
sistance in  detecting  muscular  defects,  par- 
ticularly when  used  in  conjunction  with  the 
phorometer.  Thus  employed,  it  enables  the 
patient  to  determine  when  the  streak  seen  with 
one  eye  crosses  through  the  muscle-testing 
spot-light  observable  by  the  other  eye,  as  here- 
after described. 

Procedure  for  Making  the  Muscle  Test 
The  Ski-optometer  should  be  equipped  with 
two  Maddox  rods,  one  red  and  one  white. 
Their  combined  use  is  of  the  utmost  import- 
ance since  they  assist  in  accurately  determin- 
ing cyclophoria  and  its  degree  of  tortion  as 


[45] 


Refraction    and   Muscular   Imbalance 

designated  on  the  degree  scale,  and  fully  de- 
scribed in  a  later  chapter. 

When  the  Maddox  rods  are  placed  in  a 
vertical  position,  it  is  an  indication  that  the 
vertical  muscles  are  being  tested;  when  placed 
horizontally,  the  horizontal  muscles  are  being 
tested.  It  should  be  particularly  noted  that 
the  streaks  of  light  observable  through  the 
Maddox  rods  always  appear  at  right  angles 
to  the  position  in  which  they  lie. 

The  Ski-optometer  should  be  placed  in  a 
comfortable  position  before  the  patient's  face 
with  the  brow-rest  and  pupillary  distance  ad- 
justed to  their  respective  requirements.  The 
instrument  should  be  levelled  so  that  the  bub- 
ble of  the  spirit  level  lies  evenly  between  its 
two  lines,  thus  insuring  horizontal  balance. 
The  muscle-test  light  should  be  employed  at 
an  approximate  distance  of  twenty  feet  on  a 
plane  with  the  patient's  head.  Best  results 
in  muscle  testing  are  secured  through  the  use 
of  the  Woolf  ophthalmic  bracket,  with  iris 
diaphragm  chimney  and  a  specially  adapted 
concentrated  filament  electric  lamp  (Fig. 
9).  This  gives  a  brilliant  illumination 
which  is  particularly  essential.  The  test  for 
error  of  refraction  should  be  made  in  the 
usual  manner,  using  the  spherical  and  cylin- 
drical lenses  contained  in  the  Ski-optometer, 

[46] 


Refraction   and   Muscular   Imbalance 

thus  obviating  the  transference  of  trial-case 
lenses  and  the  use  of  a  cumbersome  trial 
frame.  The  time-saving  thus  effected  enables 
the  refractionist  to  include  a  muscle  test  in 
every  examination  and  without  tiring  the  pa- 
tient— a  consideration  of  the  utmost  import- 
ance. 

Binocular  and  Monocular  Test 

The  test  for  muscular  imbalance  may  be 
divided  in  tw^o  parts.  First,  binocular  test, 
or  combined  muscle  test  of  the  two  eyes ;  sec- 
ond, monocular  test,  or  muscle  test  of  each 
eye  separately.  The  latter  does  not  signify 
the  shutting  out  of  vision  or  closing  off  of 
either  eye,  since  muscular  imbalance  can  only 
be  determined  when  both  eyes  are  open. 
These  two  tests  are  fully  explained  in  the  fol- 
lowing chapter. 


[47] 


Chapter  VI 1 

THE  BINOCULAR  MUSCLE  TEST 

Made  with  the  Maddox  Rod  and  Phorometer 

T\  IRECTING  the  patient's  attention  to  the 
usual  muscle  testing  spot  of  light,  the  red 
Maddox  rod  should  be  placed  in  operative 
position  before  the  eye,  with  the  single  white 
line  or  indicator  on  red  zero  (Fig.  IS).  The 
rods  now  lie  in  a  vertical  position. 


Fig.    15 — The  Maddox  rods  placed  vertically  denote  test 

for  right  or  left  hyperphoria,  causing  a  horizontal  streak 

to  be  seen  by  patient. 

The  pointer  of  the  phorometer  should  like- 
wise be  set  on  the  neutral  line  of  the  red  scale, 
causing  the  handle  to  point  upward  (Fig. 
16).  A  distance  point  of  light  and  a  red 
streak  laying  in  a  horizontal  position  should 
now  be  seen  by  the  patient. 


[48] 


Refraction   and  Muscular  Imbalance 


Fig.  16— The  phorometer  handle  placed  verticaUy,  de- 
notes vertical  muscles  are  undergoing  test  for  right  or 
left   hypherphoria — as   indicated   by   "R.    H."   or    "L.    H." 

Instead  of  memorizing  a  vast  number  of 
rules  essential  where  trial  case  prisms  are 
employed  for  testing  ocular  muscles,  the 
pointer  of  the  phorometer  indicates  not  only 
the  degree  on  the  red  scale,  but  the  presence  of 
right  hyperphoria  (R.  H.)  or  left  hyper- 
phoria,  (L.  H.). 


Fig.    17— The    horizontal    streak   caused    by   Maddox    rod 

bisecting  muscle  testing  spotlight  for  vertical  imbalance, 

as  patient  should  see  it. 

Assuming   that   the   patient   finds   that   the 
streak  cuts  through  the  point  of  light,  the  re- 


[49] 


Refraction   and   Muscular   Imbalance 


Fig.    18 — The   Maddox   rods   placed   horizontally  test   eso- 

phoria  or  exophoria,  caudng  a  vertical  streak  to  be  seen 

by   the    patient. 

fractionist  instantly  notes  the  absence  of  hy- 
perphoria. Should  the  point  of  light  and  the 
red  streak  not  bisect,  prism  power  must  be 
added  by  rotating  the  phorometer's  handle  to 
a  position  that  will  cause  the  streak  to  cut 
through  the  light  (Fig.  17).  While  testing 
for  hyperphoria,  the  red  scale  should  alone 
be  employed,  the  white  scale  being  totally 
ignored. 

ESOPHORIA    AND    ExOPHORIA 

The  next  step  is  to  set  the  white  lines  of  the 
red  Maddox  rod  either  at  white  zero,  or  180° 
line,  with  the  rods  in  a  horizontal  position 
(Fig.  18)  and  the  phorometer  on  the  white 
neutral  line,  with  handle  horizontal,  (Fig. 
19),   thus  making  the   test  for   esophoria  or 


[50] 


Refraction    and   Muscular   Imbalance 

exophoria,  technically  known  as  lateral  devia- 
tions. 

The  red  streak  will  now  be  seen  in  a  verti- 
cal position.  Should  it  bisect  the  spot  of  light, 
it  would  show  that  no  lateral  imbalance  ex- 
ists. Should  it  not  bisect,  the  existence  of 
either  esophoria  or  exophoria  is  proven,  ne- 
cessitating the  turning  of  the  phorometer 
handle.  Should  the  refractionist  rotate  the 
handle  in  a  direction  opposing  that  of  the  ex- 
isting imbalance,  the  light  will  be  taken  fur- 
ther away  from  the  streak,  indicating  that  the 
rotation  of  the  prisms  should  be  reversed. 

At  the  point  of  bisection  (Fig.  20),  the 
phorometer  will  indicate  on  the  white  scale 


Fig.   19 — The  phorometer  handle   placed  horizontally  de- 
notes   horizontal    muscles    are    undergoing    test    for    eso- 
phoria or  exophoria  indicated  by  "Es."  or  "Ex." 

[51] 


Refraction    and   Muscular   Imbalance 

whether  the  case  is  esophoria  or  exophoria  and 
to  what  amount.  In  testing  esophoria  (ES) 
or  exophoria  (EX),  the  white  scale  is  alone 
employed,  no  attention  being  given  to  the  red 
scale. 


Fig.  20 — The  vertical  streak  bisecting  muscle  testing  spot- 
light for  horizontal  inmbalance,  as  patient  should  see  it. 

Making    Muscle   Test   Before   and   After 
Optical  Correction 

It  is  considered  best  to  make  the  binocular 
test  before  regular  refraction  is  made,  mak- 
ing note  of  the  findings;  and  again  repeating 
the  test  after  the  full  optical  correction  has 
been  placed  before  the  patient's  eye.  This 
enables  the  refractionist  to  definitely  deter- 
mine whether  the  correction  has  benefited  or 
aggravated  the  muscles.  Furthermore,  by 
making  the  muscle  test  before  and  after  the 
optical  correction,  a  starting  point  in  an  ex- 
amination   is    frequently    attained.      For   ex- 

[52] 


Refraction   and   Muscular   Imbalance 


ample,  where  the  phorometer  indicates  eso- 
phoria  it  is  usually  associated  with  hyper- 
opia, whereas  exophoria  is  usually  asso- 
ciated with  myopia,  thus  serving  as  a  clue  for 
the  optical  correction. 

Assuming  for  example  that  the  binocular 
muscle  test  shows  six  degrees  of  esophoria 
without  the  optical  correction,  and  with  it  but 
four  degrees,  it  is  readily  seen  that  the  im- 
balance has  been  benefited  by  the  optical  cor- 
rection. Under  such  conditions  it  is  safe  to 
believe  that  the  optical  correction  will  con- 
tinue to  benefit  as  the  patient  advances  in 
years,  tending  to  overcome  muscular  defect. 

When  to  Consider  Correction  of  Muscular 
Imbalance 

In  correcting  an  imbalance,  it  is  also  a  good 
plan  to  adhere  to  the  following  rule:  In  case 
of  hyperphoria,  either  right  or  left,  consider 
for  further  correction  only  those  cases  that 
show  one  degree  or  more.  In  exophoria, 
those  showing  three  degrees  or  more.  In  eso- 
phoria, correct  those  showing  five  degrees  or 
more,  except  in  children,  where  correction 
should  be  made  in  cases  showing  an  excess  of 
3°  of  esophoria.  These  rules  are  naturally  sub- 
ject to  variation   according  to   the   patient's 

[53] 


Refraction    and   Muscular   Inihalan 


ce 


refraction  and  age,  but  they  are  generally  ac- 
cepted as  safe. 

Four  Methods  for  Correction  of  Muscular 
Imbalance 

There  are  four  distinct  methods  for  correct- 
ing muscular  imbalance,  each  of  which  should 
be  carried  out  in  the  following  routine: 

1.  Optical  correction  made  with  spheres 
or  cylinders,  or  a  combination  of  both. 

2.  Muscular  exercising  or  "ocular  gym- 
nastics." This  is  accomplished  on  the  same 
principle  as  the  employment  of  other  forms  of 
exercises,  or  calisthenics. 

3.  The  use  of  Prisms:  When  the  second 
method  fails,  prisms  are  supplied,  with  base 
of  prism  before  the  weak  muscle,  for  rest 
only. 

4.  Operation  :  If  the  above  three  methods, 
as  outlined  in  the  following  chapters,  have 
been  carefully  investigated,  nothing  remains 
but  a  tetonomy  or  advancement,  or  other  op- 
erative means  for  relief  and  satisfaction  to 
the  patient. 

The  Rotary'  Prism 

The  rotary  prism  of  the  Ski-optometer, 
(Fig.  21)  consists  of  a  prism  unit,  having  a 
total  equivalent  of  thirty  degrees.  It  is  com- 
posed of   two  fifteen-degree   prisms,  back  to 


[54] 


Refraction   and   Muscular   Imbalance 

back,  so  that  the  turn  of  its  pinion  or  handle 
causes  each  of  its  lenses  to  revolve,  one  on  the 
other.  When  its  bases  are  opposite,  they  neu- 
tralize; when  directly  together,  they  give  a 
total  value  of  thirty  degrees.  While  revolv- 
ing from  zero  to  maximum  strength,  they  give 
prism  values  w^hich  are  indicated  on  the  scale 
of  measurements,  the  red  line  denoting  the 
total  prism  equivalent. 


Fig.    21 — Turning   rotary   prism's    pinioned    handle    gives 

prism  value  from  zero  to  30°   as  indicated  by  prism's  red 

line  indicator. 

It  is  obviously  essential  to  know^  where  the 
base  of  the  rotary  prism  is  located.  Therefore 
if  prism  in  or  out  is  desired,  the  zero  gradua- 
tions should  be  placed  vertically  and  the  red 
line  or  indicator  set  at  the  upper  zero  (Fig. 
21). 

A  rotation  inward  to  10  would  give  a  prism 


[55] 


Refraction   and   Muscular   Imbalance 

equivalent  of  ten  degrees,  base  in.  A  rotation 
from  zero  to  10  outward  would  give  a  prism 
equivalent  of  ten  degrees,  base  out,  etc.  With 
zero  graduations  horizontal  and  the  red.  line 
or  indicator  set  therewith,  a  rotation  upward 
to  ten  on  the  scale  would  give  a  prism  equi- 
valent of  ten  degrees,  base  up.  A  rotation 
from  zero  downward  to  10  would  give  a 
prism  equivalent  of  ten  degrees,  base  down. 
An  understanding  of  the  foregoing  will 
show  that  a  rotation  of  the  red  line,  or  indica- 
tor, will  give  prism  value  from  zero  to  30, 
with  base  up,  down,  in  or  out. 

Use  of  the  Rotary  Prism  in  Binocular 
Muscle  Tests 

Should  a  case  be  one  of  esophoria,  exceed- 
ing the  ten  degree  range  of  the  phorometer, 
the  rotary  prism  should  be  brought  into  opera- 
tive position  with  cypher  (0)  graduations 
vertical  (Fig.  21),  while  the  red  line  or 
indicator  should  be  set  at  10  on  the  outer  or 
temporal  scale.  The  phorometer's  indicator 
should  again  be  set  on  the  center  or  neutral 
line  on  the  white  scale.  The  rotary  prism 
will  then  add  ten  degrees  to  the  esophoria 
reading  indicated  on  the  phorometer. 

Should  the  case  be  one  of  exophoria,  exceed- 
ing ten  degrees,  the  indicator  should  be  set 

[56] 


Refraction   and  Muscular  Imbalance 

at  ten  degrees  upon  the  inner  or  nasal  scale 
and  the  indicator  of  the  phorometer  should 
then  be  set  at  the  white  center  or  neutral  line, 
as  in  the  previous  test.  Should  prism  power 
ever  be  required  to  supplement  the  phoro- 
meter in  hyperphoria,  the  rotary  prism  should 
be  employed  with  zero  graduations  horizontal, 
and  the  red  line  or  indicator  set  at  ten  degrees 
on  upper  or  lower  scale,  as  required. 


[57] 


Chapter  VIII 

THE  MONOCULAR  DUCTION  MUSCLE  TEST 

Made  with   Both   Rotary  Prisms 

AXT'HILE  the  previously  described  binocular 
muscle  test  made  with  the  phorometer  and 
Maddox  rod,  only  determines  the  existence 
and  amount  of  esophoria,  exophoria,  and 
hyperphoria,  neither  the  faulty  nor  the  deviat- 
ing muscle  is  located,  hence  a  monocular 
muscle  test  is  essential  in  order  to  determine 
whether  the  muscles  of  the  right  or  left  eye 
are  faulty.  Furthermore,  an  imbalance  may 
possibly  be  due  to  either  a  faulty  muscular 
poise,  or  lack  of  nerve  force  in  one  or  both 
eyes.  A  "duction  test"  should  accordingly 
be  made  of  each  muscle  of  each  eye  separately, 
followed  by  a  comparison  of  the  muscular 
pull  of  both  eyes  collectively. 

These  tests  are  commonly  termed  adduc- 
tion, abduction,  superduction  and  subduc- 
tion,  and  are  defined  in  the  order  named. 
They  include  tests  of  the  vertical  and 
horizontal  muscles  of  each  eye,  made  in- 
dividually by  means  of  the  rotary  prisms,  each 
being  placed  before  the  eye  undergoing  the 
test. 

Locating  the  Faulty  Muscle 

The    phorometer    and     the     Maddox    rod 


[58] 


Refraction   and  Muscular  Inibalan 


a 


should  be  removed  from  operative  position, 
discontinuing  the  use  of  the  muscle-testing 
spot-light,  employed  in  the  previously  de- 
scribed binocular  test.  The  optical  correction, 
if  one  is  required,  should  be  left  in  place,  while 
the  patient's  attention  should  be  directed,  W\\h 
both  eyes  open,  to  the  largest  letter  on  the 
distant  test  chart;  or  if  preferable,  the  Greek 
cross  in  the  Woolf  opthalmic  chimney  may  be 
used.  Either  one,  however,  should  be  located 
on  a  plane  with  the  patient's  head.  As  a  guide 
for  the  operator,  it  might  be  well  to  remember 
that  when  the  handle  of  the  rotary  prism  is  in 
a  horizontal  position,  the  lateral  or  horizontal 
muscles  are  being  tested.  On  the  other  hand, 
when  the  handle  is  in  a  vertical  position,  the 
vertical  muscles  are  undergoing  the  test. 

Adduction 

Adduction,  or  relative  convergence,  is  the 
power  of  the  internal  muscles  to  turn  the  eyes 
inward;  prism  power  base  out  and  apex  m, 
is  employed. 

To  test  adduction  of  the  patient's  right  eye, 
the  rotary  prism  should  be  placed  in  position 
before  the  right  eye,  the  red  line  or  prism  in- 
dicator being  registered  at  zero  upon  the 
prism  upper  scale.  The  two  cyphers  (0) 
should  be  placed  in  a  vertical  position  with 

[59] 


Refraction    and  Muscular   Imbalance 


Fig.  22 — To  test  adduction,  base  out  is  required.     Rotary 
prism's  line  or  indicator  should  be  rotated  from  zero  out- 
wardly.    To   test   abduction,    base   in   is   required.      Indi- 
cator   should    be    rotated    inwardly    from    zero. 


the  handle  pointed  horizontally  (Fig.  21). 
The  rotary  prism  should  then  be  rotated  so 
that  its  red  line  or  indicator  is  rotated  out- 
ward from  zero  until  the  large  letter — pre- 
ferably the  largest  letter,  which  is  usually  ''E" 
— on  the  distance  test-type  or  the  Greek  cross 
previously  referred  to,  first  appears  to  double 
in  the  horizontal  plane.  The  reading 
on  the  scale  of  measurements  should  ac- 
cordingly be  noted.  This  test  should  be  re- 
peated several  times,  constantly  striving  for 
the  highest  prism  power  that  the  patient  will 
accept  without  producing  diplopia.  The 
prism  equivalent  thus  obtained  will  indicate 


[60] 


Refraction   and  Muscular  Imbalance 


the  right  adduction  and  should  be  so  re- 
corded, as  designated  in  Fig.  24.  The  amount 
of  adduction  ranges  from  6  to  28,  prism  di- 
optres, the  normal  average  being  24. 

Abduction 

Abduction  is  the  relative  power  of  the  ex- 
ternal muscles  to  turn  the  eyes  outward. 
Prism  power  base  in  and  apex  out  is  em- 
ployed. To  determine  abduction,  or  the 
amount  of  divergence  of  the  external  rectus 
muscle  of  the  right  eye,  prism  power  with 
base  in  or  toward  the  nasal  side  should  be 
employed.  The  rotary  prism  will  therefore 
remain  in  the  same  relative  position  as  in 
making  the  adduction  test  (Fig.  22),  with 
the  two  cyphers  (0)  or  zero  graduations 
vertical,  but  the  indicator  or  red  line  should 
be  rotated  inward  from  zero,  or  towards  the 
patient's  nose. 

With  the  patient's  attention  again  directed 
to  the  large  letter  ''E,"  or  the  Greek  cross,  this 
inward  rotation  should  be  continued  until 
diplopia  or  double  vision  occurs.  Like  the 
former,  this  test  should  be  repeated  several 
times,  the  ref ractionist  continuing  to  strive  for 
the  highest  prism  power  which  the  eye  will  ac- 
cept. This  will  indicate  abduction  of  the  right 
eye  and  should  be  so  recorded  as  designated  in 


[61] 


Refraction    and   Muscular   Imbalance 

Fig.  24.  The  amount  of  abduction  ranges 
from  3  to  10  prism  dioptres.  The  normal  av- 
erage is  8. 

The  ratio  of  adduction  to  abduction  is  nor- 
mally rated  at  about  three  to  one.  In  other 
words,  it  is  conceded  that  the  power  of  the 
eye  to  converge  is  normally  three  times  as 
great  as  its  power  to  diverge,  the  usual  mea- 
surements being  eight  to  twenty-four  respec- 
tively. While  applicable  in  most  instances, 
this  may  vary  in  different  cases. 

SUPERDUCTION 

Superduction,  sometimes  termed  sursum- 
duction,  is  the  relative  power  of  the  superior 
recti  to  turn  the  eyes  upward.  Prism  power 
base  down  and  apex  up  is  employed.  To 
test  superduction,  the  rotary  prism  should  be 
placed  in  position  with  the  two  cyphers 
lying  horizontally,  with  the  handle  pointed 
vertically  (Fig.  23).  The  patient's  atten- 
tion should  again  be  directed  to  the  large 
letter  "E'\  and  the  indicator  or  red  line 
should  be  rotated  downward  from  zero.  The 
highest  prism  power  that  the  patient  will  ac- 
cept before  the  object  appears  to  double  in 
the  vertical  plane  will  indicate  the  degree  of 
right  superduction.  This  should  be  recorded 
accordingly.     Conditions  of  this  kind  do  not 


[62] 


Refraction   and  Muscular  Imbalance 

usually  exceed  two  or  three  degrees.  The 
test,  however,  should  be  repeated  several 
times  before  the  final  result  is  recorded,  as 
indicated  in  Fig.  24.  The  amount  of  super- 
duction  ranges  from  1  to  4  prism  dioptres. 
The  normal  average  is  2. 


Fig.    23— To    test    superduction,    base    down    is    required. 
Rotary  prism's  line  or  indicator  should  be  rotated  down- 
ward from  zero.     To  test  subduction,  base  up  is  required. 
Indicator  should  be  rotated  upward  from  zero. 

Subduction 

Subduction,  sometimes  termed  infraduc- 
tion  or  deorsumduction,  is  the  relative  power 
of  the  inferior  recti  to  turn  the  eyes  downward. 
Prism  power  base  up  and  apex  down  is  em- 
ployed. To  test  subduction,  the  rotary  prism 
should    be    operated    with    zero    graduations 

[63] 


Refraction   and  Muscular  Imbaland 


placed  horizontally,  as  in  the  superduction 
test  (Fig.  23),  but  the  indicator  should  be 
slowly  rotated  in  the  reverse  direction,  or  up- 
ward from  zero.  With  the  patient's  attention 
again  directed  to  the  large  letter  ''E,"  or  the 
Greek  cross,  the  strongest  degree  prism  thus  se- 
cured without  diplopia  will  indicate  the  right 
subduction.  The  amount  of  subduction  ranges 
from  1  to  4  prism  dioptres.  The  normal  av- 
erage is  2. 

Any  difference  between  superduction  and 
subduction,  usually  denoting  the  existence  of 
hyperphoria,  should  be  given  careful  con- 
sideration. 

Procedure  for  Monocular  Muscle  Testing 

As  previously  explained,  after  a  duction 
test  of  each  of  the  four  muscles  of  the  right 
eye,  the  rotary  prism  before  that  eye  should 
be  placed  out  of  position  and  the  procedure 
for  adduction,  abduction,  superduction  and 
subduction  repeated  by  means  of  the  rotary 
prism  before  the  left  eye.  In  case  of  an  ex- 
isting imbalance,  after  testing  the  muscle  of 
both  right  and  left  eyes,  the  refractionist  can 
quickly  determine  which  muscle  or  muscles 
may  be  lacking  in  strength  (Fig.  24).  In 
practically  every  instance  muscle  exercises  or 
correcting    prisms    may    then    be    prescribed 

[64] 


Refraction   and  Muscular  Imbalance 


with  definite  knowledge  of  requirements,  as 
further  described  in  the  following  para- 
graphs. 

A  binocular  muscle  test  made  with  the 
phorometer,  Maddox  rod  and  distant  mus- 
cle -  testing  point  of  light  might  quickly 
indicate  six  degrees  of  exophoria,  both  be- 
fore and  after  the  optical  correction  is  made. 
While  this  would  doubtless  be  the  correct 
amount  of  the  manifest  imbalance,  it  would 
be  a  difficult  matter  to  ascertain  which  mus- 
cles caused  the  disturbance.  To  determine 
this  important  question,  the  monocular  or 
duction  test  should  be  invariably  employed. 

Diagnosing  a  Specific  Muscle  Case 

Assuming,  for  example,  a  specific  case 
where  six  degrees  of  exophoria  was  deter- 
mined in  the  binocular  test  that  the  muscle 
findings  in  the  duction  test  show  right  adduc- 
tion of  twenty-four  degrees,  with  an  accom- 
panying abduction  of  eight  degrees;  likewise 
a  superduction  and  subduction  of  two  degrees 
for  each  eye.  With  the  aid  of  a  chart  or 
diagram— which  should  be  made  in  every 
case — a  comparison  of  these  figures  would 
indicate  an  exophoria  of  approximately  six 
degrees,  with  a  corresponding  weak  left 
internus    (Fig.    24).     This    not   only   shows 

[65] 


Refraction   and  Muscular  Imbalance 

the  muscle  pull  of  each  eye  individually,  but 
a  comparison  of  the  two  eyes  as  indicated  by 
the  dotted  lines.  Thus  the  relationship  of  the 
two  eyes,  and  their  corresponding  muscles  is 
quickly  indicated. 


Equal 


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Fig.  2A — Duction  chart  should  be  made  in  every  case.  Above 
readily  shows  existence  of  muscular  imbalance  and  proves 
subduction  and  superduction  for  both  eyes  are  equal;  other- 
wise hypherphoria  would  be  disclosed.  Also  note  ab- 
duction for  both  right  and  left  eye  are  equal,  otherwise 
esophoria  would  be  disclosed.  Also  note  adduction  for 
right  eye  is  24°  while  left  is  but  18°,  proving  a  case  of 
6°  of  exophoria  with  a  left  weak  internus. 

A  glance  at  the  above  diagram  discloses 
the  following  three  important  facts,  all  of 
which  should  be  known  to  the  refractionist 
before  a  single  thought  can  be  devoted  to  the 
correcting  of  the  case: 

1.  6°  exophoria  is  the  amount  of  the  in- 
sufficiency. 

2.  18°  adduction    (which  should  be  24°). 

3.  Left  weak  internus. 


[66] 


Refraction   and  Muscular  Imbalance 

As  previously  stated,  the  power  to  con- 
verge is  normally  rated  3  to  1,  or  8  to  24,  as 
shown  above,  while  the  power  of  the  eye  to 
look  upward,  is  equal  to  the  power  to  look 
downward.  The  diagram  accordingly  proves 
that  the  muscles  of  the  right  eye  are  in  perfect 
balance,  having  equal  muscular  energy. 

A  comparison  of  the  left  eye  shows  adduc- 
tion of  18  degrees  with  an  abduction  of  8  de- 
grees, proving  a  lateral  insufficiency  because 
the  ratio  is  less  than  3  to  1  ;  and  the  muscles 
of  the  left  eye  are  at  fault.  The  power  of  2 
degrees  superduction  and  2  degrees  subduc- 
tion,  proves  that  no  weakness  exists  in  the  ver- 
tical muscles. 

After  making  the  duction  test  for  each  eye 
individually,  a  comparison  of  both  eyes  in  re- 
lationship to  each  other  may  be  more  readily 
determined  by  following  the  dotted  lines 
(Fig.  24). 

As  previously  stated,  it  is  the  inability  of 
the  two  eyes  to  work  together  that  causes  the 
imbalance,  so  that  if  both  eyes  were  normal, 
the  adduction,  abduction,  superduction  and 
subduction    of  the  two  e^^es  would  agree. 

The  duction  chart  (Fig.  24.)  also  shows 
that  the  corresponding  muscles  of  each  eye 
agree — with  the  exception  of  the  adduction 

[67] 


Refraction   and  Muscular  Imbalance 

of  the  right  eye  and  the  left  eye.  This  proves 
that  the  left  internus  is  weak,  measuring  only 
18  degrees  instead  of  24  degrees;  it  further 
proves  the  6  degrees  of  exophoria  in  the 
monocular  test,  as  w^as  quickly  and  more 
readily  determined  in  the  binocular  test. 

Likewise,  in  cases  of  esophoria,  hyper- 
phoria, or  cataphoria,  the  making  of  definite 
muscle  measurements  independently  through 
the  prescribed  method  would  show  through 
the  merest  glance  at  a  similar  diagram  which 
muscle  or  muscles  were  relatively  out  of  bal- 
ance. Heterphoria  of  almost  any  type,  or 
tendencies  other  than  normal,  may  be  fully 
investigated  by  making  a  thorough  and  sepa- 
rate test  of  each  muscle. 

Where  an  imbalance  exists,  a  rapid  test  may 
be  employed  to  distinguish  a  pseudo  or  false 
condition  from  a  true  condition.  This  is  ac- 
complished by  first  placing  the  two  Maddox 
rods  (both  the  red  and  white)  so  that  the  rods 
lie  in  a  vertical  position.  If  the  two  lines  fuse, 
we  have  determined  the  existence  of  a  false 
condition  caused  by  a  possible  error  of  refrac- 
tion or  nerve  strain.  If  the  lines  separate,  we 
have  determined  a  true  muscular  condition, 
and  then  only  should  the  second  method  of 
muscular  treatment  follow. 


[68] 


Same  as  Model  2i^ 
but  Automatic 
Cylinder    Arrange- 
ment omitted. 


Ski-optometer  Model  205 

Embodying:  Spherical  Lenses  Combined  with  Appliances 
for  Testing  and  Correcting  Muscular  Imbalance. 


[69] 


T 


Chapter  IX 

FIRST  m?:thod  of  treatment  _ 

OPTICAL  CORRECTION 

^HE  mere  determination  of  the  degree  of 
an  imbalance,  or  even  the  diagnosis  of  a 
patient's  trouble,  is  not  sufficient.  If  relief  is 
to  be  secured,  something  more  must  be  ac- 
complished. 

As  previously  stated,  muscular  imbalance 
may  be  corrected  through  one  of  the  four  fol- 
lowing rules  or  methods,  each  explained  in 
their  relative  order: 

1 — Optical  Correction 
2 — Muscular  Exercise 
3 — Use  of  Prism  Lenses 
-Operative  Methods 


ESOPHORIA 

To  correct  a  case  of  muscular  imbalance, 
where  six  degrees  of  esophoria  has  been  de- 
termined, the  first  rule  of  making  the  test  for 
optical  correction  with  the  Ski-optometer's 
spherical  and  cylindrical  lenses,  would  be  in 
the  line  of  routine.  The  binocular  test  made 
with  the  phorometer  and  combined  use  of  the 
red  Maddox  rod  would  have  determined  the 
six  degrees  of  esophoria. 


[70] 


Refraction   and  Muscular  Imbalance 

The  reason  for  making  the  binocular  muscle 
test  before  and  after  the  optical  correction  is 
because  an  imbalance  is  often  aggravated  or 
benefited  by  the  correcting  lenses.  The 
optical  correction  frequently  eliminates  the 
need  for  further  muscular  treatment. 

For  example,  we  will  assume  that  the 
optical  correction  tends  to  decrease  the  degree 
of  esophoria  from  six  degrees  to  four  degrees. 
According  to  the  previously  mentioned  rule 
for  correcting  cases  exceeding  one  degree  in 
hyperphoria,  three  degrees  in  exophoria  and 
five  degrees  in  esophoria,  the  condition  would 
indicate  that  of  being  "left  alone."  Just  what 
is  taking  place  should  be  fully  understood — 
its  cause  as  well  as  its  efifect. 


Perfectly  centered  L 
pupil 


Centered  pupil  and 
decentered  lens 


Centered  lens  and  decentered 
pupil 


Fig.  25 — Comparative  diagram  showing  how  a  decentered 

lens    before    a    centered    eye    has    the    same    effect    as    a 

centered  lens  before  a  decentered  eye. 

When  not  otherwise  specified,  accurately 
centered  lenses  are  of  primary  importance. 
The  pupil  of  the  eye  should  be  directly  be- 
hind the  center  of  each  lens  (Fig.  25). 


[71] 


Refraction   and  Muscular   Imbalance 

Figure  ''A"  of  the  latter  sketch  illustrates 
a  perfectly  centered  lens — its  center  indicated 
by  a  cross,  the  circle  representing  an  eye  di- 
rectly behind  it.  Figure  "B"  illustrates  a  per- 
fectly centered  pupil  behind  a  prism,  with  its 
center  designated  by  a  cross.  To  ascertain 
how  the  centered  spherical  lens  takes  the  place 
of  a  prism.  Figure  ''C"  should  be  compared 
with  Figure  ''B";  this  will  show  that  the  eye 
is  decentered,  while  the  lens  is  centered.  A 
further  comparison  will  prove  that  the  results 
in  Figures  "B"  and  ''C"  are  identical,  the 
correcting  lenses  having  practically  the  same 
effect  through  the  decentration  of  the  eye  as 
if  a  prism  were  prescribed,  nature  supplying 
its  own  decentration. 

Treatment    for   Correcting    Esophoria    in 
Children 

In  case  of  esophoria,  regardless  of  amount, 
slightly  increased  spherical  power  is  fre- 
quently prescribed  for  children.  This  will 
naturally  blur  or  fog  the  patient's  vision,  but 
in  their  effort  to  overcome  the  blur,  accommo- 
dation is  relaxed,  usually  tending  to  correct 
the  muscular  defect. 

In  such  cases,  as  a  rule,  a  quarter  diopter 
increased  spherical  strength  may  frequently 
be  added  for  each  degree  of  esophoria  as  de- 


[72] 


Refraction   and  Muscular   Imbalance 

termined  before  the  optical  correction  was 
made.  In  a  case  of  6  degrees  of  esophoria, 
the  refractionist  may  prescribe  +1.50  dioptre 
spherical  added  to  the  optical  correction, 
which,  let  us  assume,  is  +1.00  sph.  = — 1.00 
cyl.  ax.  180°,  so  that  the  treatment  glasses  would 
be  +2.50  sph.  =  —1.00  ax.  180°  (See  Pro- 
cedure on  Page  74). 

At  the  end  of  each  three  months'  period,  the 
patient  should  be  requested  to  return,  when 
the  binocular  and  the  duction  test  should  again 
be  made,  comparing  results  with  the  work  pre- 
viously accomplished.  An  improvement  tend- 
ing to  build  up  the  left  weak  externus  will 
possibly  permit  of  a  decrease  of  the  excessive 
spherical  power,  so  that  excessive  spherical 
power  is  reduced  until  completely  removed, 
in  all  probability  overcoming  the  muscular 
defect.  Esophoria  is  almost  invariably  a  false 
condition  and  frequently  is  outgrown  under 
this  treatment  as  the  child  advances  in  years. 
On  the  other  hand,  esophoria  uncared  for  in 
the  child  may  tend  to  produce  exophoria  in 
the  adult. 


[73] 


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[74] 


Chapter  X 

SECOND  METHOD  OF  TREATMENT- 
MUSCULAR  EXERCISE 

Made  With   Two  Rotary  Prisms  and   Red 
Maddox  Rod 


Exophoria 

IF  a  case  is  one  of  exophoria  of  six  degrees, 
where  the  second  method  of  treatment  or 
muscular  exercise  is  in  line  of  routine,  it  is 
essential  to  first  determine  through  a  duction 
test  and  the  preparation  of  the  diagram  ex- 
actly which  one  of  the  four  muscles  are  faulty 
(Fig.  24). 

Having  determined,  with  the  aid  of  the  dia- 
gram, first,  the  existence  of  6  degrees  of  ex- 
ophoria; second,  18  degrees  of  adduction; 
third,  a  weak  left  internus — the  next  proced- 
ure is  to  determine  what  degree  of  prism  will 
enable  the  patient  to  obtain  single  binocular 
vision,  with  both  eyes  looking  ''straight." 

To  determine  this,  place  both  of  the  Ski- 
optometer's  rotary  prisms  in  position  with  the 
handle  of  each  pointing  outward  horizontally. 
The  red  line  or  indicator  of  each  prism  should 
then  be  placed  at  30°  of  the  outer  scale 
(Fig.  26). 

The  red  Maddox  rod  should  be  horizontally 
[75] 


Refraction   and  Muscular  Imbalance 

positioned  before  the  eye,  the  white  line  on 
indicator  pointing  to  180°  of  the  scale  (Fig. 
27).  The  strength  of  the  rotary  prism  before 
the  right  eye  should  thereupon  be  reduced  by 
rotating  the  prism  indicator  or  red  line  toward 
the  upper  zero  (0)  to  a  point  where  the  pa- 
tient first  sees  the  red  streak — assuming  that 
the  red  line  appears  at  42  degrees,  that  is  30 
degrees  before  the  left  eye  and  12  degrees  be- 
fore the  right. 


A  B 

Fig.   26    (A    and   B)— First   position   of   rotary   prisms   to 

determine   amount  of  prism   exercise   to  be   employed   for 

building  up  the  weak  muscle. 

The  prism  should  then  be  still  further  re- 
duced until  the  vertical  streak  produced  by 
the  Maddox  rod  directly  bisects  the  muscle 
testing  spot  of  light.    Assuming  that  this  point 


[76] 


Refraction   and  Muscular   Imbalance 

be  thirty-eight  degrees,  which  is  four  degrees 
less,  single  binocular  vision  is  produced. 


Fig.  27 — Position  of  red  Maddox  rod  used  in  conjunction 
with  Fig.  2G  for  prism  exercising. 

For  example,  sixty  degrees  of  prism  power 
(the  combined  power  of  the  two  rotary 
prisms)  will  usually  cause  complete  distor- 
tion. Therefore,  as  outlined  in  Figure  28, 
the  patient,  seeing  only  out  of  the  right  eye, 
will  detect  nothing  but  a  white  light.  By 
gradually  reducing  the  strength  of  the  prism 
before  the  right,  which  is  the  good  eye,  the 
patient  will  eventually  see  a  red  streak  off  to 
the  left.  A  continued  and  gradaal  reduction 
to  a  point  where  the  red  streak  bisects  the 
white  light,  will  determine  how  much  prism 
power  is  required  for  the  patient  to  obtain 
single  bmocular  vision,  thus  establishing  the 


[77] 


Refraction   and  Muscular  Imbalance 

same  image  at  the  same  time  on  each  fovea  or 
retina  (Fig.  20). 

This  has  taught  the  patient  to  do  that  which 
he  has  never  before  accomplished.  There- 
fore, after  having  been  taught  how  to  make 
the  two  eyes  work  in  relation  to  each  other, 
the  natural  tendency  thereafter  will  be  to 
strive  for  the  same  relationship  of  vision  with 
both  eyes.  The  refractionist  should  then  aim 
to  reduce  the  excessive  amount  of  prism  re- 
quired to  give  binocular  vision,  which  can  be 
accomplished  by  muscular  exercise. 

It  must  always  be  remembered  before  the 
refractionist  is  ready  to  employ  the  muscular 
exercise  or  second  method,  that  the  degree  of 
prism  required  to  give  the  patient  single  bi- 
nocular vision  must  be  determined  with  the 
optical  correction  in  place.  The  exercise  must 
be  practised  daily  in  routine,  a  daily  record 
being  essential. 

An  Assumed  Case 

We  will  assume  a  case  where  42  degrees  is 
required  to  enable  the  patient  to  first  see  the 
red  streak  as  produced  by  the  Maddox  rod  to 
the  extreme  left.  Through  a  continued  grad- 
ual reduction  of  4  degrees  (or  to  38  degrees), 
we  next  learn  that  the  streak  was  carried  over 
until  it  bisected  the  white  spot  of  light,  giving 


[78] 


Refraction    and   Muscular    Inibaland 


single  binocular  vision  and  producing  a  posi 
tion  of  rest. 


Fig.   28 — Simplified   chart   showing  the    prism    action   em- 
ployed in  developing  a  weak  ocular  muscle  through  alter- 
nating prism  exercise.     Either  side  of  38°  in  excess  of  4 
causing  diplopia. 


The  patient  has  now  established  the  limita- 
tion of  the  exercise,  which  is  four  degrees, 
this  limitation  being  determined  by  the  dif- 
ference between  the  point  where  the  streak 
was  first  seen  to  the  extreme  side  and  where  it 
bisected  the  spot.  The  same  amount  of  four 
degrees  should  then  be  used  for  the  opposite 


[79] 


Refraction   and  Muscular   Imbalance 

side,  thus  reducing  the  prism  strength  to  34 
degrees. 

This  again  produces  diplopia,  because  of 
the  lesser  amount  of  prism  power  employed 
to  give  single  binocular  vision.  The  refrac- 
tionist  should  then  return  to  38  degrees,  where 
single  binocular  vision  had  originally  been 
determined  (Fig.  28),  alternating  back  to  42, 
returning  to  38,  over  to  34,  back  to  38,  and  so 
on.  This  procedure  should  be  employed  once 
a  day  just  after  meals  for  about  five  minutes, 
and  repeated  ten  times,  constantly  striving  for 
a  slight  reduction  of  prism  power  from  day 
to  day. 

Effect  of  Muscular  Exercise 

This  muscular  treatment,  or  constructive 
exercising,  should  enable  the  patient  to  over- 
come his  amount  of  four  degrees  in  either  di- 
rection in  about  a  week.  Hence  in  the  case 
showing  38  degrees  for  single  binocular  vision, 
results  may  be  looked  for  in  about  nine  weeks 
— four  degrees  divided  into  38  degrees.  While 
the  patient  is  undergoing  the  treatment,  which 
is  nothing  more  than  the  strengthening  of  the 
interni  muscles  or  developing  adduction,  it 
is  natural  to  believe  that  the  amount  of  im- 
balance is  likewise  being  conquered.  This, 
however,  is  readily  determined  from  time  to 


[80] 


Refraction   and  Muscular  Imbalance 

time  by  making  the  binocular  muscle  test  with 
the  phorometer  and  Maddox  rod,  as  well  as 
the  duction  chart  test  (Fig.  24),  as  previously 
outlined. 

To  fully  appreciate  the  effect  of  this  muscu- 
lar treatment,  the  reader  need  only  hold  his 
head  in  a  stationary  position,  casting  his  eyes 
several  times  from  the  extreme  right  to  the 
extreme  left,  not  failing  to  note  the  apparent 
muscular  strain.  On  the  other  hand,  with  the 
aid  of  the  Ski-optometer's  rotating  prisms,  the 
refractionist  not  only  has  complete  control  of 
the  patient's  muscles  at  all  times,  but  scien- 
tifically accomplishes  muscular  exercise  with- 
out any  tiresome  strain,  overcoming  all  pos- 
sible exertion. 

After  the  case  in  question  has  been  reduced 
to  30  degrees,  having  no  further  use  for  the 
rotary  prism,  it  may  be  removed  from  before 
the  right  eye  and  the  same  exercising  proce- 
dure continued  as  before  with  the  remaining 
left  side  rotary  prism  by  reducing  its  power, 
until  it  is  likewise  down  to  zero. 

Having  reduced  both  prisms  to  zero,  each 
prism  should  again  be  placed  in  position  with 
zero  graduations  vertical  and  the  prism  in- 
dicator on  upper  zero.  Both  prisms  should 
then  be  turned  simultaneously  about  four  de- 
grees toward  the  nasal  side  of  the  patient,  thus 

[81] 


Refraction    and   Muscular    Imbalance 

tending  to  jointly  force  corresponding  muscles 
of  both  eyes. 

Home  Treatment  for  Muscular  Exercise — 

Square    Prism    Set    Used    in    Conjunction 

With   the   Ski-Optometer 

Where  a  patient  is  unable  to  call  each  day 
for  this  muscular  treatment  or  exercise,  the 
work  will  be  greatly  facilitated  by  employing 
a  specially  designed  set  of  square  prisms  rang- 
ing in  strength  from  J4  to  20  degrees  for  home 
treatment.  As  in  the  case  previously  cited,  it 
is  necessary  to  carefully  instruct  the  patient 
that  the  interni  muscles  must  be  developed, 
hence  prism  base  out  with  apex  in  must  be 
employed.  Attention  should  then  be  directed 
to  a  candle  light,  serving  as  a  muscle  testing 
spot  of  light  and  stationed  in  a  semi-dark  room 
at  an  approximate  distance  of  twenty  feet. 

Having  determined  through  the  Ski-opto- 
meter  the  strength  of  the  prism  required  after 
each  office  treatment,  its  equivalent  should 
then  be  placed  in  a  special  square  prism  trial 
frame  which  permits  rotation  of  the  prism, 
although  the  patient  is  frequently  taught  to 
twirl  the  lens  before  the  eye.  This  exercise 
may  be  continued  for  about  five  minutes  each 
day. 

The  patient  should  also  be  instructed  to  call 

[82] 


Refraction    and  Muscular   Imbalance 

at  the  end  of  each  week,  when  the  work  may 
be  checked  by  means  of  the  Ski-optometer's 
rotary  prisms,  making  the  duction  test  as 
previously  explained  and  outlined  in  Fig.  24. 
It  is  then  possible  to  determine  whether  or  not 
satisfactory  results  are  being  obtained.  Other- 
wise the  exercise  should  be  abandoned. 

Should  the  second  method  employed  in  the 
work  of  muscular  imbalance  not  prove  effec- 
tive, the  third  method  requiring  the  use  of 
prisms  would  be  next  in  routine. 


[83J 


Chapter  XI 

THIRD  METHOD  OF  TREATIVIENT— 

PRISM  LENSES 

When  'and   How   Employed 

A  S  Stated  in  the  preceding  chapter,  on  as- 
certaining the  failure  of  the  second 
muscular  treatment  or  method,  prisms  are  em- 
ployed for  constant  wear.  When  prism  lenses 
are  used,  whether  the  case  is  exophoria  or 
esophoria,  or  right  or  left  hyperphoria,  it  is 
always  safe  to  prescribe  one-quarter  degree 
prism  for  each  degree  of  prism  imbalance  for 
each  eye.  For  example,  in  a  case  of  6  degrees 
of  esophoria,  a  prism  of  1^  degree  base  out 
should  be  prescribed  for  each  eye;  or  in  6  de- 
grees of  exophoria,  employ  the  same  amount 
of  prism,  but  base  in.  In  right  hyperphoria, 
place  the  prism  base  down  before  the  right  eye 
and  up  before  the  left,  and  vice  versa  for  left 
hyperphoria. 

It  is  not  always  advisable,  however,  to  allow 
the  patient  to  wear  the  same  degree  of  prism 
for  any  length  of  time.  Many  authorities  sug- 
gest a  constant  change  with  the  idea  that  a 
prism  is  nothing  more  than  a  crutch.  Should 
the  same  degree  be  constantly  worn,  even 
though  it  afforded  temporary  relief,  the  eye 
would  become  accustomed  to  it  and  the  pur- 

[84] 


Refraction    and   Muscular   Imhahui 


cc 


pose  of  the  prism  entirely  lost.  Prisms  should 
be  prescribed  with  extreme  care,  their  use  be- 
ing identical  with  that  of  dumb-bells,  where 
weight  is  first  increased  to  maximum  and  sub- 
sequently reduced,  viz. : 

•     Prism   Reduction   Method 

Where  prisms  are  prescribed,  it  is  con- 
sidered good  practice  to  make  a  binocular 
muscle  test  and  the  duction  test  (Fig.  24) 
at  the  end  of  each  three  months'  period,  em- 
ploying the  phorometer,  Maddox  rod,  and 
rotary  prisms,  as  already  explained. 

If  the  condition  shows  any  decrease,  the 
prism  degree  should  be  proportionately  de- 
creased. For  example,  in  the  case  originally 
showing  6  degrees  of  exophoria,  one-quarter 
degree  prism  for  each  degree  of  imbalance 
was  prescribed,  or  1^  degree  for  each  eye. 
If  the  same  case  subsequently  indicated  4  de- 
grees, only  one  degree  for  each  eye  should  be 
prescribed — and  so  on,  a  gradual  reduction  of 
prism  value  being  constantly  sought. 

Except  in  rare  cases,  prisms  should  not  be 
prescribed  with  the  base  or  apex  at  oblique 
angles,  as  the  eye  is  rarely  at  rest  with  such  a 
correction.  An  imbalance  may  be  caused  by 
a  false  condition  in  one  rectus  and  a  true  im- 
balance in  the  other,  giving  one  the  impres- 


[85] 


Refraction    and   Muscular   Imbalan 


ce 


sion  that  cyclophoria  exists,  as  explained  in  a 
following  chapter. 

Having  now  employed  the  three  methods, 
the  refractionist  can  readily  understand  that 
a  marked  percentage  of  muscular  imbalance 
cases  may  be  directly  benefited  through  the 
aid  of  the  Ski-optometer.  If  these  three 
methods  of  procedure  fail,  there  is  nothing 
left  but  the  fourth  and  last  method — that  of 
operative  procedure. 


[86] 


Chapter  XII 

A  CONDENSATION  OF  PREVIOUS  CHAPTERS 
ON  THE  PROCEDURE  FOR  MUSCLE  TEST- 
ING WITH   THE  SKI-OPTOMETER 

T^HE  present  chapter,  intended  for  those 
desiring  a  synopsis  or  condensed  sum- 
mary of  muscular  imbalance  work,  should 
prove  of  the  utmost  assistance  to  the  busy  re- 
f  ractionist.  Muscular  imbalance  work  can  be 
successfully  conducted  if  the  following  routine 
is  studied  and  memorized,  with  the  Ski-optom- 
eter  constantly  before  the  reader.  The  chapters 
containing  the  corresponding  figures  and  dia- 
grams or  illustrations  will  then  be  readily 
comprehended.  It  is  also  important  to  care- 
fully note  the  captions  under  each  diagram. 

1.  Without  any  testing  lenses  before  pa- 
tient's eyes,  direct  attention  to  a  20-foot  distant 
muscle  testing  spot  of  light  (Fig.  9). 

2.  Place  phorometer  handle  vertically 
(Fig.  16). 

Place  red  Maddox  rod  vertically  (Fig.  15). 
Patient  should  see  a  white  spot  of  light,  and  a 
red  horizontal  streak  (Fig.  17). 

Simply  turn  phorometer  handle  until  hori- 
zontal streak  bisects  white  spot  of  light.  Point- 
er then  indicates  amount  of  deviation  on  red 
scale.    Ignore  cases  less  than  1°  hyperphoria, 


[87] 


Refraction   and   Muscular   Imbalance 


whether  right  or  left  designated  by  (R.  H. — 

L.  H.). 

3.  Place  phorometer  handle  horizontally 

(Fig.  19). 

Place  red  Maddox  rod  horizontally  (Fig. 
18).  Patient  should  see  a  white  spot  ^f  light 
and  a  vertical  red  streak  (Fig.  20). 

Simply  turn  phorometer  handle  until  red 
streak  bisects  spot  of  light.  Pointer  indicates 
amount  of  deviation  on  white  scale,  whether 
esophoria  or  exophoria  designated  by  (Es — 
Ex). 

4.  Ignore  all  exophoria  cases,  less  than  3°. 

Ignore  all  esophoria  cases,  less  than  S° — ex- 
cept in  children,  ignore  less  than  3°  of  eso- 
phoria. 

5.  Always  make  the  above  or  binocular 
muscle  test — with  phorometer  and  red  Mad- 
dox before  optical  correction  or  (test  for 
spheres  and  cylinders)  and  again  after  optical 
correction  where  case  shows  more  than  1-3-5 
rule,  to  determine  whether  muscles  are  aggra- 
vated or  benefited. 

6.  In  cases  showing  more  than  the  1-3-5 
rule,  shown  in  above  No.  4,  make  monocular 
duction  test  first  with  rotary  prism  before  pa- 
tient's right  eye, — then  with  rotary  prism  be- 
fore left  eye  to  find  faulty  muscle  and  de- 
termine which  eve  is  aflfected. 


[88] 


Refraction    and   Muscular   Imbalance 

7.  To  test  adduction,  prism  base  out  is  re- 
quired. Rotary  prism's  red  line  or  indicatoi 
should  be  rotated  from  zero  outwardly.  To 
test  abduction,  base  in  is  required.  Indicator 
should  be  rotated  inwardly  from  zero  (Fig. 
22).  Power  of  adduction  as  compared  with 
abduction,  is  normally  3  to  1 — usually  rated 
24  to  8. 

8.  To  test  superduction,  base  down  is  re- 
quired. Rotary  prism's  line  or  indicator 
should  be  rotated  downward  from  zero.  To 
test  subduction,  base  up  is  required.  Indica- 
tor should  be  rotated  upward  from  zero. 
Power  of  superduction  as  compared  with  sub- 
duction, is  normally  equal— usually  rated  2  for 
each  (Fig.  23). 

9.  Direct  patient's  attention  to  largest  let- 
ter on  distant  chart,  usually  letter  ''E,"  rotat- 
ing red  line  indicator  of  rotary  prism  outlined 
in  above  No.  7  and  No.  8,  until  diplopia  is 
first  procured. 

10.  The  use  of  a  duction  chart  on  a  record 
card,  quickly  designates  pull  for  each  of  four 
muscles  (Fig.  24),  illustrating  an  assumed 
case  of^ 

1st — 6D  of  Exophoria. 

2nd — 18°   adduction    (which   must  be  devel- 
oped to  24°). 
3rd — Patient  has  a  left  weak  internus. 


im 


Refraction    and   Muscular   Imbalance 

11.  Employ  First  Method — Optical  Cor- 
rection— to  effect  treatment. 

12.  Assuming  a  case  of  a  child  with  6°  of 
esophoria — 8°  of  right  abduction  and  2°  left 
abduction  indicating  a  left  weak  externus,  pre- 
scribe a  quarter  dioptre  increased  plus  spheri- 
cal power  for  each  degree  of  imbalance,  thus 
adding+1.50D  spherical  to  optical  correction. 
This  is  the  first  method  of  treatment.  This 
requires  a  thorough  reading  of  Chapter  IX 
on  Treatment  for  Correcting  Esophoria  in 
Children  and  a  careful  study  of  the  formula. 
For  synopsis  see  Page  74. 

Four  Methods  of  Treating  an  Imbalance 
Case  When  the  Preceding  One  Fails 

1st — Optical  correction; 

2nd — Muscular  exercise  or  treatment; 
75%  ARE  Curable  with  First  and  Second 
Methods. 

3rd — Prisms; 

5%  ARE  Curable  with  Third  Method. 
4th — Operation ; 

20%  ARE  Curable  with  Fourth  Method. 

13.  When  first  method  of  treatment  fails, 
Employ  Second  Method — Muscular  Exer- 
cise— to  efifect  treatment. 

1st — Find  degree  of  prism  patient  will  ac- 


[90] 


Refraction    and   Muscular   Imbalance 

cept  to  produce  single  binocular  vision  with 
optical  correction  on,  placing  both  rotary 
prisms  in  position,  handles  horizontal,  red  line 
on  30°  of  temporal  scale  of  each,  giving  total 
value  to  60°  (Fig.  26a  and  b). 
2nd — Also  place  red  Maddox  rod  before 
patient's  eye  (rods  horizontal)  (Fig.  18),  call- 
ing patient's  attention  to  usual  muscle  testing 
spot  of  light. 

3rd — Reduce  prism  before  good  eye  un- 
til red  streak  appears,  noting  degree  (which 
we  assume  show^s  42°  the  combined  total  value 
of  both  prisms)  slowly  continue  to  decrease 
prism  until  streak  bisects  spot.  Assume  this 
shows  total  of  38°.  Either  side  of  38°  in 
excess  of  4°  (38  to  42)  produces  diplopia. 
Prisms  must  only  be  rotated  from  38°  to 
42°  back  to  38°  over  to  34°— back  to  38"  over 
to  42° — back  again  to  38°  and  so  on — exercise 
to  be  continued  daily  ten  times  for  five  minutes 
(Fig.  28). 

4th — At  end  of  each  week,  duction  test 
should  again  be  made.  Duction  chart  should 
show  a  tendency  to  reduce  exophoria  by  a 
gradual  building  up  of  adduction,  approxi- 
mately one  week  is  usually  sufficient  to  teach 
patient  to  hold  streak  within  the  spot  (be- 
tween 38°  and  42°).  Exercise  to  be  contin- 
ued until  both  prisms  are  worked  down  to 

[91] 


Refraction   and  Muscular   Imbalance 

zero.  Exercise  tends  to  teach  patient  how 
to  establish  same  image  on  each  fovea  or  re- 
tina at  same  time. 

Sth — If  patient  is  unable  to  call  daily  for 
treatment,  employ  home  treatment.  (Read 
''Home  Treatment  for  Muscular  Exercising," 
Page  82). 

Employ  Third  Method — Use  of  Prisms 
for  Constant  Wear  to  effect  treatment. 

Prisms 

1st.  Where  a  case  cannot  be  reduced 
through  use  of  first  two  methods,  as  for  exam- 
ple in  a  case  of  6°  of  exophoria,  prescribe  1/4 
of  amount  of  imbalance  (>4  ><  6  =  1>4°)  for 
each  eye — base  in — or  esophoria  base  out,  hy- 
perphoria base  up  on  eye  affected. 

2nd.  Advise  patient  to  call  every  three 
months  and  make  duction  test  (Fig.  24). 
If  no  improvement  in  condition,  after  wearing 
prisms  six  months,  operative  means  is  suggest- 
ed. 

Assume  a  case  is  benefited,  reduce  prism 
power  according  to  rule;  J/4D  prism  for  each 
degree  of  imbalance. 

Cyclophoria 
This  work  being  of  a  technical  nature,  it  is 
deemed  best  for  the  reader  to  study  Chapter 
XIII  and  XIV. 


[92] 


Chapter  XIII 

CYCLOPHORIA 
Made  with   Maddox  Rods  and  Rotary  Prisms 

/^YCLOPHORIA,  a  condition  affecting 
the  oblique  muscles  of  the  eye,  is  caused 
by  its  rotation.  It  is  detected  in  the  following 
manner  by  the  combined  use  of  the  red  and 
white  Maddox  rods  and  the  rotary  prism. 


Fig.  29 — Position   of  rotary  prism  for  producing  diplopia 
in   testing  cyclophoria   with   prism   placed    at   8°    base   up. 

Darken  the  room  and  direct  the  patient's 
attention  to  the  usual  muscle-testing  spot  of 
light,  located  approximately  twenty  feet  away 
and  on  a  direct  plane  with  the  patient's  eye. 
The  optical  correction,  if  one  is  required, 
should  always  be  left  in  place — just  as  in  mak- 
ing other  previously  described  muscle  tests. 


[93] 


Refraction   and  Muscular  Imbalance 

The  rotary  prism  should  then  be  brought  be- 
fore the  patient's  right  eye  with  the  handle- 
pointing  upward  and  with  zero  graduations 
horizontal.  The  indicator  or  red  line  should 
then  be  rotated  upward  from  zero  to  eight 
upon  the  prism  scale,  creating  the  equivalent 
of  a  prism  of  8  diopters  with  base  up  (Fig. 
29) .  This  normally  caused  diplopia,  although 
in  some  cases  it  may  be  necessary  to  place  the 
prism  at  10  or  12  degrees  before  diplopia  is 
produced. 


A  B 

Fig.  30 — (A.  and  B.) — First  position  of  both  Maddox  rods 

used     in     conjunction     with     Fig.     29     for     determining 

cyclophoria. 

The  red  Maddox  rod  should  then  be 
brought  into  operative  position  before  the  pa- 
tient's left  eye  (Fig.  30a)  and  the  white  Mad- 
dox rod  before  the  patient's  right  eye,  (Fig. 
30b)   setting  each  one  so  that  the  rods  lie  in 


[94] 


Refraction   and   Muscular   Imbalan 


ce 


a  vertical  position  with  their  white  line  on  the 
large  red  zero  (0). 

The  patient  should  now  see  two  separate 
and  distinct  streaks  of  light,  one  appearing 
below  the  other. 


DETERMINING    CYCLOPHORIR 

/?/GHn  £r£  ^Eirr  £/£ 

Fig.    31  ^'9.    34 


A/O     CrCLO/^HO^/ff 


/VO    CYCLOPHO/?//^ 


Fuj.    32 

crcL  op/io/^/ff 


Fw-    35 
■hCYCLOPHOP/ff 


Fig.   n 

crcLOH/-<oR/n 


Fig.    Z6 
CYCLOPHO/^tR 


Figs.    31-36 — Diagram    showing    how    streaks    appear    to 

patient,    as  produced   by  the   Maddox  rods  in  testing  for 

cyclophoria. 

Should  there  be  no  cyclophoria  of  the  right 
eye,  the  streaks  will  appear  in  a  horizontal 
plane  parallel  to  each  other  (Fig.  31). 


[95] 


Refraction    and  Muscular  Imbalance 

Should  the  red  streak  appear  horizontally 
to  the  left  eye,  and  the  white  streak  seen  by 
the  right  eye  appear  at  an  angle  therewith, 
cyclophoria  of  the  right  eye  would  be  in- 
dictated  (Fig.  32). 

In  brief, should  the  white  streak  dip  towards 
the  patient's  left  side,  the  case  would  be  one  of 
right  plus  cyclophoria  (Fig.  32)  ;  whereas 
right  minus  cyclophoria  would  be  indicated 
should  the  white  streak  dip  to  the  patient's 
right  side  (Fig.  33). 

Next,  setting  the  rotary  prism  of  8  degrees, 
placed  base  up  before  the  patient's  left  eye, 
the  red  streak  should  appear  below  the  white 
one.  Should  the  two  streaks  appear  hori- 
zontally, parallel  with  each  other,  there  would 
be  no  cyclophoria  of  the  left  eye  (Fig.  34). 

If,  however,  the  upper  or  white  streak 
should  appear  horizontal,  and  the  lower  or 
red  streak  at  an  angle  therewith  dipping 
toward  the  patient's  right  side,  the  left  eye 
would  be  cyclophoric  and  the  case  would  be 
one  of  left  plus  cyclophoria,  as  the  chart  in- 
dicates (Fig.  35). 

Should  the  red  streak  dip  in  toward  the 
patient's  left  side,  \th-minus  cylophoria  would 
be  designated  (Fig.  36). 

The  patient  would  instinctively  describe, 
with  pointed  finger  and  hand  motion,  the  posi- 

[96] 


Refraction    and   Muscular   Imbalance 


tion  of  the  '^dipping"  line  just  as  one  would 
describe  a  spiral  staircase.  Should  this  test 
determine  that  no  cyclophoria  exists  in  either 
eye,  there  would  be  no  necessity  for  further 
tests. 

Some  authorities  claim  that  both  Maddox 
rods  should  be  of  the  same  color,  so  as  to  more 
readily  assist  the  patient  to  fuse  the  two  objects. 
If  the  reader  so  desires,  he  can  readily  place 
a  red  lens  from  the  trial  case  in  the  forward 
cell  of  the  instrument. 

The  characters  plus  and  minus  in  cyclo- 
phoria merely  refer  to  plus  as  signifying  a 
tendency  toward  the  temporal  side;  minus  in- 
dicating a  tendency  toward  the  nasal  side. 
This  has  no  bearing  on  ''convex"  and  ''con- 
cave," which  are  frequently  designated  as 
"plus"  and  "minus." 

The  test  for  cyclophoria  is  particularly  es- 
sential, proving  of  utmost  importance  where 
the  patient  requires  an  astigmatic  correction 
with  the  cylinder  axis  in  oblique  meridian. 
The  case  should  then  be  investigated  in  every 
instance  by  making  a  thorough  and  separate 
test  of  each  eye  for  cyclophoria. 

In  a  case  where  cyclophoria  is  determined, 
the  trouble  may  be  caused  by  the  functioning 
of  other  muscles,  through  the  drain  of  nerve 


[97] 


Refraction    and   Muscular   Imbalaud 


force,  thus  disturbing  the  harmony  of  every 
muscle  action. 

Cyclophoria  is  frequently  caused  by  an  im- 
balance of  two  recti,  giving  an  oblique  pull. 
In  most  cases,  it  is  merely  necessary  to  release 
the  torsion,  as  described  in  the  following 
chapter. 


[98] 


Chapter  XIV 

CYCLODUCTION  TEST 

Made  With  the  Combined  Use  of  the  Two 
Maddox  Rods 

LJAVING  determined  that  cyclophoria  ex- 
ists, as  previously  outlined,  the  next  step 
would  be  to  make  a  cycloduction  test,  or  a  test 
of  the  oblique  muscles  individually.  Maddox 
rods,  both  red  and  white,  should  be  placed  in 
position  with  the  rods  horizontal — the  plus  and 
minus  sign  at  90  degrees  on  the  scale  (Fig. 
37).  The  patient's  attention  should  be  direct- 
ed to  the  usual  muscle-testing  spot  of  light, 
when  a  vertical  band  of  light  will  appear  to 
the  patient,  as  shown  in  Fig.  38. 


Fig.  37 — (A.  and  B.) — Primary  position  of  combined   use 
of   both  Maddox   rods   for   determining  cycloduction   test. 


[99] 


Refraction    and    Muscular    Imbalance 


AfO/?r7flL 


j^/GHT  ^crcLODUcT/o/^   RiCHT  -crCLODucr/OAf 
lEFr    -  CrCLODOCTJO/^  LEFT   -^-crcLODucr/o/^/ 


Figs.    38-40 — Diagram    showing   position   of    streaks    pro- 
duced   by    Maddox    rods    as    they    appear    to    patients    in 
making  cycloduction  tests. 

To  measure  the  duction  range  of  the  in- 
ferior oblique  of  the  right  eye,  it  is  merely 
necessary  to  slowly  rotate  the  Maddox  rod 
before  the  right  eye  upward  at  its  nasal  end  to 
the  point  where  the  band  of  light  breaks  so  as 
to  resemble  a  letter  "X'\  This  gives  in  de- 
grees the  amount  of  right  plus  cycloduction, 
as  indicated  on  the  temporal  scale,  when  it 
will  appear  to  the  patient,  as  shown  in  Fig.  39. 

The  Maddox  rod  should  then  be  restored 
to  its  original  position,  with  the  plus  and  minus 
on  the  90  degree  line  of  the  scale  (Fig.  37), 
and  rotated  upward  at  the  temporal  end  until 
it  again  takes  the  form  of  the  letter  ''X."  (Fig. 
40.)  The  position  of  the  indicator  will  now  de- 
note the  amount  of  right  minus  cycloduction, 
or  duction  range  of  the  right  superior  oblique 
muscles.      Having    determined    the    duction 


[100] 


Refraction    and   Muscular   Imbalan 


ce 


range  of  the  oblique  muscles  of  the  patient's 
right  eye,  both  Maddox  rods  should  be  placed 
in  original  position  with  rods  horizontal  and 
plus  and  minus  sign  on  90°  of  scale,  as  shown 
in  Fig.  37. 

The  Maddox  rod  before  the  left  eye  is  then 
employed  exactly  in  the  same  manner  as  be- 
fore when  the  test  for  the  right  eye  was  made. 
A  plus  cycloduction  of  the  left  eye  would  be 
indicated,  as  shown  in  Fig.  40,  while  a  minus 
cycloduction  of  the  left  eye  would  appear  to 
the  patient,  as  show^n  in  Fig.  39. 

By  recording  a  comparison  of  each  eye,  as 
explained,  it  will  be  found  that  the  range  of 
duction  usually  averages  five  to  twenty  degrees 
on  either  side  of  the  90  degree  line,  as  indi- 
cated on  the  scale  surrounding  the  Maddox 
rods. 

It  will  be  recalled  that  cyclophoria  was  only 
to  be  looked  for  in  oblique  astigmatic  cases. 
It  is  frequently  possible  to  correct  the  patient's 
trouble,  by  changing  the  axis  of  the  cylinder, 
before  one  or  both  eyes,  a  minus  cycloduction 
signifying  a  change  of  axis  towards  180°  while 
a  plus  toward  90°,  according  to  the  amount 
lacking  in  full  duction  power.  It  is  also  well 
to  exercise  the  oblique  muscles  through  a  ro- 
tation of  the  Maddox  rod  before  the  affected 
eye,  whether  it  be  one  or  both  that  is  lacking 


[101] 


Refraction    and   Muscular   Imbalance 


in  full  duction  power,  until  the  required 
amount  is  reached  to  equal  its  fellow  member. 
For  a  more  exhaustive  treatise  the  author 
suggests  a  reading  of  Dr.  Savage's  work 
on  the  subject. 

Treatment  for  Cyclophoria 
As  previously  stated,  it  often  proves  of  great 
benefit  to  employ  a  muscular  exercise  where  a 
patient  has  an  existing  cyclophoria  of  either 
one  or  both  eyes,  results  derivable  through  the 
exercise  of  the  recti  muscles  having  been  pre- 
viously detailed. 

To  exercise  the  oblique  muscles  of  the  right 
eye,  both  Maddox  rods  should  be  placed  in 
the  original  position  employed  for  making 
cycloduction  test,  as  previously  explained 
(Fig.  37).  This  causes  the  patient  to  see  but 
one  band  or  vertical  streak  (Fig.  38). 

The  Maddox  rod,  placed  before  the  right 
eye,  should  be  slowly  rotated  inward  from 
ninety  degrees  to  a  point  on  the  scale  where  the 
single  streak  of  light  breaks,  when  it  should 
again  be  returned  to  ninety  degrees.  This 
causes  a  contraction  and  relaxation  of  the  mus- 
cles in  the  form  of  an  exercise  and  should  be 
repeated  ten  times — about  five  minutes  each 
day.     By  employing  the  Maddox  rod  before 

[102] 


Refraction    and   Muscular   Imbalance 

the  left  eye  in  precisely  the  same  manner,  its 
oblique  muscles  will  be  exercised. 

To  determine  whether  or  not  this  form  of 
exercise  is  beneficial  to  the  patient,  the  weekly 
cycloduction  test,  as  previously  described, 
should  be  made  and  compared  with  the  origi- 
nal findings. 


[103] 


A  Co?npact 
Phorometer  and 
Trial  Frame. 


Ski-optometer  Model  235 

For  Testing  and   Correcting   Muscular  Imbalance- 
Providing  a  Comfortable  Form  of  Trial  Frame. 


[104] 


Chapter  XV 

MOVEMENTS  OF  THE  EYEBALLS  AND 
THEIR  ANOMALIES 

A  FTER  a  careful  study  of  the  foregoing 
'^chapters,  the  refractionist  may  desire 
further  knowledge  concerning  muscular  im- 
balance— a  matter  in  which  the  Ski-optometer 
plays  an  exceptionally  important  part. 

It  should  be  remembered  that  it  is  only  the 
general  utility  of  the  instrument,  plus  one's 
knowledge  of  refraction  and  individual  diag- 
nosis that  enables  the  refractionist  to  attain 
maximum  efficiency  in  every  examination,  a 
fact  which  largely  accounts  for  the  following 
chapter. 

Monocular  Fixation 

When  we  view  an  object  directly,  so  that  it 
appears  to  be  more  distinct  than  surrounding 
objects,  we  are  said  to  "fix"  or  "fixate''  it. 

As  the  fovea  is  normally  the  most  sensitive 
part  of  the  retina,  affording  by  far  the  most 
distinct  vision,  "fixation,"  in  the  great  major- 
ity of  cases,  is  so  performed  that  the  image  of 
the  object  that  is  "fixated"  falls  upon  the  fovea 
of  the  eye  that  is  "fixing."  This  is  known  as 
central  or  muscular  "fixation." 

When  central  vision  is  absent,  however,  the 
patient  is  compelled  to  see  with  a  portion  of 

[105] 


Refraction    and   Muscular   Imbalance 

the  retina  outside  of  the  fovea.  The  eye  must 
then  be  so  directed  as  to  cause  the  image  of 
the  object  to  fall  on  this  outlying  portion  of 
the  retina.  This  is  termed  "eccentric  fixa- 
tion," and  usually  denotes  that  vision  is  excep- 
tionally poor. 

The  ability  to  ''fix"  is  apparently  acquired 
in  early  infancy  by  constant  practice  in  look- 
ing at  objects.  Any  marked  interference  with 
vision,  particularly  with  central  vision — pres- 
ent at  birth  or  soon  thereafter— will  tend  to 
prevent  the  acquisition  of  this  ability,  and  in 
extreme  cases  the  eye  does  not  learn  to  ''fix" 
at  all,  but  aimlessly  wanders  in  all  directions. 

Binocular  Fixation 

We  habitually  use  the  eyes  together,  fixat- 
ing with  both  at  once;  that  is,  we  direct  the 
eyes  in  such  a  way  that  the  image  of  the  object 
to  which  the  attention  is  directed  falls  on  the 
fovea  of  each  eye. 

Where  both  eyes  are  accurately  directed  to 
an  object  at  which  one  or  both  are  looking,  the 
condition  is  known  as  "binocular  fixation," 
which  is  commonly  understood  to  mean  that 
both  eyes  are  straight. 

The  ability  to  produce  and  maintain  binoc- 
ular fixation — to  keep  both  eyes  directly 
straight — is  acquired  early  in  life.     The  im- 

[106] 


Refraction    and  Muscular   Imbalance 

pulse  to  maintain  it  grows  with  exercise,  and 
soon  becomes  so  strong  that  after  the  age  of 
infancy  binocular  fixation  is  present  in  the 
great  majority  of  persons,  and  in  most  of  them 
is  present  all  the  time. 

Binocular  fixation  must  be  distinguished 
through  three  conditions  —  orthophoria, 
heterophoria  and  squint. 

Orthophoria 

This  is  the  condition  in  which  both  eyes 
look  straight  at  the  same  object,  whether  both 
see  it  or  not.  There  is  not  the  slightest  ten- 
dency of  deviation. 

Heterophoria 

This  is  the  condition  in  which  both  eyes 
keep  looking  straight  at  the  same  object  so 
long  as  both  see  it;  but  as  soon  as  one  eye  is 
excluded  from  vision  (as  by  a  screen)  that  eye 
deviates.  This  is  then  a  tendency  of  deviation 
which  is  strong  enough  to  become  manifest 
when  either  eye  is  covered,  but  which  is  abol- 
ished or  overcome  by  the  compelling  impulse 
of  binocular  fixation  as  soon  as  both  eyes  are 
used  for  seeing.  A  heterophoria  thus  pro- 
duces a  maximum  deviation.  The  deviation 
is  also  said  to  be  latent,  since  it  is  absent  under 
ordinary  conditions  and  is  brought  to  light 

[107] 


Refraction    and   Muscular   Imbalan 


ce 


only  under  special  conditions.  A  common 
though  improper  term  for  heterophoria  is 
''insufficiency." 

Squint 

Squint  is  the  condition  in  which  there  is 
so  great  a  tendency  to  deviation  that  even  vs^hen 
both  eyes  are  uncovered,  one  deviates  and  only 
one  "fixes."  It  differs,  therefore,  from  hetero- 
phoria in  that  the  deviation  it  produces  is  ob- 
vious under  ordinary  conditions. 

Squint  is  also  called  strabismus,  or  hetero- 
tropia.  In  other  v^ords,  in  orthophoria  there 
is  binocular  fixation  all  the  time  and  under  all 
conditions;  in  heterophoria  it  is  present  only 
when  the  two  eyes  are  uncovered,  so  that  both 
see  the  object  looked  at;  while  in  squint  it  is 
not  present  at  all. 

Or,  in  still  plainer  terms,  in  orthophoria 
both  eyes  are  straight  all  the  time;  in  hetero- 
phoria both  are  straight,  but  only  so  long  as 
both  are  uncovered;  and  in  squint  only  one 
eye  is  straight,  no  matter  whether  both  eyes 
are  uncovered  or  not. 

In  squint,  while  binocular  fixation  is  alto- 
gether absent,  the  ability  to  perform  monocu- 
lar fixation  is  almost  always  preserved;  i.e., 
the  squinting  eye  will  "fix"  at  once  if  the  other 
eye    is    covered.      It    is    only    when    there    is 

[108] 


Refraction    and  Muscular   Imbalan 


ce 


marked  amblyopia,  particularly  as  the  result 
of  a  central  scotoma  (or  spot  on  the  cornea 
in  the  line  of  vision)  that  the  squinting  eye 
loses  its  power  to  fix  at  all,  and  wanders  un- 
certainly about,  receiving  impressions  now  on 
one,  now  on  another  portion  of  the  retina. 

The  term  imbalance  is  often  used  to  denote 
the  two  conditions  opposed  to  orthophoria; 
i.e.,  to  denote  collectively  heterophoria  and 
squint. 

Varieties  of  Heterophoria  and  Squint 

1.  Classification  According  to  Direction  of 
Deviating  Eye :  Heterophoria  and  squint  may 
be  classified  according  to  the  direction  as- 
sumed by  the  deviating  eye.  Thus  we  have 
the  following  varieties  of  heterophoria: 

Heterophoria 

Lateral   Deviations 
Either  eye   deviates 

In,  or  toward  the  nose  Esophoria 

Out,  or  toward  the  temple  Exophoria 

Vertical   Deviations 

The  right  eye  goes  up  and  the  left  down Right  Hyperphoria 

The  left  eye  goes  up  and  the  right  down Left  Hyperphoria 

In  rare  cases  of  vertical  heterophoria,  each 
eye  has  either  an  upward  tendency  (anopho- 
ria)  or  a  downward  tendency  (cataphoria) . 
These  cases  must  not  be  confused  with  ^natro- 
pia  and  catatropia.     In  anaphoria  :and  cato- 

[109] 


Refraction    and   Muscular    Imbalance 

phoria,  there  is  binocular  fixation  when  both 
eyes  are  uncovered,  while  in  anatropia  and 
catatropia  one  of  the  eyes  squints.  This  shows 
the  following  squint  condition: 

Squint 

Lateral  Squint 
The  deviating  eye  turns  in,  or  toward  the  nose: 

Esotropia   (Strabismus  convergens — Convergent  Squint) 
The  deviating  eye  turns  out  or  toward  the  temple: 

Exotropia    (Strabismus  divergens — Divergent  Squint) 

Vertical  Squint 
The  deviating  eye  turns  up: 

Hypertropia   (Strabismus  sursumvergens)    (Right  or  left) 
The  deviating  eye  turns  down: 

Hypotropia    (Strabismus  deorsumvergens)    (Right  or  left) 

In  addition  to  these  lateral  and  vertical  de- 
viations, conditions  exist  in  which  the  verti- 
cal meridian  of  one  eye,  instead  of  maintain- 
ing its  parallelism  with  the  vertical  meridian 
of  the  other,  either  forms  (or  tends  to  form) 
an  angle  with  it  (cyclotropia) ,  but  is  kept 
in  position  through  muscular  effort  (cyclo- 
phoria.) 

Cyclotropia  is  usually  due  to  paralysis  of 
one  of  the  ocular  muscles,  causing  the  vertical 
meridian  of  the  affected  eye  to  be  tilted  out  or 
toward  the  temple  (extorsion)  or  in  toward 
the  nose  (intorsion).  A  tilting  of  the  vertical 
meridian  toward  the  right  is  also  called  dex- 
trotorsion  (or  positive  declination)  ;  and  to  the 
left,  levotorsion  or  negative  declination. 

[110] 


Refraction    and   Muscular   Imbalance 

2.  Constant,  Intermittent  and  Periodic 
Deviations:  A  deviation,  whether  squint  or 
heterophoria,  may  be  present  at  all  times 
(constant),  or  occasionally  present  and  occa- 
sionally absent  (intermittent).  In  this  case 
we  may  have  heterophoria  alternating  with 
orthophoria,  or  heterophoria  alternating  with 
squint;  or  squint  alternating  with  orthophoria. 
We  also  find  variations  such  as  a  squint  for 
near  and  a  heterophoria  or  orthophoria  for 
distance;  or  a  heterophoria  for  near  and  or- 
thophoria for  distance;  or  a  constant  squint 
for  near  and  an  intermittent  squint  for  dis- 
tance, etc.  Again,  a  deviation  may  be  period- 
ic, in  that  its  amount  for  distance  may  greatly 
exceed  that  for  near,  or  vice  versa. 

Opposed  to  a  periodic  deviation  is  one 
which  is  present,  and  in  about  equal  amount, 
both  for  distance  and  near.  Such  a  deviation, 
whether  squint  or  heterophoria,  is  called 
'^continuous." 

3.  Alternating  and  Uniocular  Squint:  An 
alternating  squint  is  one  in  which  when  both 
eyes  are  uncovered,  so  that  both  have  a  chance 
to  "fix";  sometimes  the  right  eye  will  deviate, 
sometimes  the  left.  In  uniocular  (less  proper- 
ly monocular)  squint,  under  the  same  condi- 
tions, one  eye,  either  the  right  or  the  left,  al- 
ways ''fixes"  and  the  other  always  deviates. 

[Ill] 


Refraction    and  Muscular   Imbalance 

A  uniocular  squint  is  denoted  as  right  or  left, 
according  to  whether  it  is  the  right  or  left  eye 
which  deviates. 

4.  Comitant  and  Non-Comitant  Devia- 
tions: In  some  varieties  of  heterophoria  and 
squint,  the  amount  of  deviation  is  the  same  in 
all  directions  of  the  gaze,  so  that  the  angle 
between  the  visual  line  of  one  eye  and  that  of 
the  other  remains  the  same,  no  matter  which 
way  the  eyes  are  turned.  Such  deviations  are 
called  comitant  or  non-comitant,  because  one 
eye  accompanies  and  keeps  pace  with  the 
other  in  all  its  movements.  In  other  cases, 
the  deviation  changes  as  the  eyes  are  moved 
in  different  directions,  so  that  the  angle  be- 
tween the  two  visual  lines  constantly  varies. 
Such  deviations  are  termed  concomitant. 
Usually  in  a  non-comitant  squint  the  angle  of 
deviation  increases  in  a  regular  way  as  the  eyes 
are  moved  in  one  direction  and  decreases  as 
they  move  in  the  direction  opposite. 

In  cases  of  long  standing,  however,  the 
squinting  eye,  particularly  when  very  ambly- 
opic, wanders  in  an  uncertain  way  and  appar- 
ently quite  without  reference  to  the  move- 
ments of  the  other  eye. 


[113] 


Chapter  XVI 
LAW  OF  PROJECTION 

nr^HE  movements  of  the  eye  are  designed 
primarily  to  effect  fixation — that  is,  to 
bring  upon  the  macula  the  image  of  the  ob- 
ject that  we  wish  to  look  at.  When  this  has 
been  accomplished,  we  know  as  a  result  of 
long  experience,  the  direction  of  the  object 
looked  at  and  also  direction  of  other  neighbor- 
ing objects.  This  knowledge  is  doubtless  af- 
forded us,  in  part,  by  our  muscle  sense.  Thus 
we  know  that  an  object.  A,  is  straight  in 
front  of  us  because  we  can  see  it  sharply  with- 
out moving  either  the  head  or  the  eyes  from 
the  position  of  rest  or  equilibrium;  and  we 
know  that  an  object,  B,  is  on  the  right  of  us 
because  to  see  it  sharply  we  have  to  move 
either  the  head  or  the  eyes  to  the  right,  thus 
altering  the  muscular  condition  from  one  of 
rest  to  one  of  tension.  But  without  moving 
either  head  or  eye,  we  also  know,  while  still 
looking  at  A,  that  B  is  to  the  right,  for  the 
image  of  B  is  then  formed  on  a  portion  of  the 
retina  situated  to  the  left  of  the  macula.  From 
long  experience  we  also  know  that  an  image 
so  situated  means  an  object  placed  on  our 
right.  Moreover,  the  farther  to  the  left  of 
the  macula  the  image  B  is,  the  farther  to  the 
right  do  we  judge  B  itself  to  be. 

[114] 


Refraction    and   Muscular   Imbalancr 

Similarly,  if  B  is  so  placed  that  its  image 
falls  below  the  macula,  we  then  know  B  it- 
self is  really  above  A,  which  forms  its  image 
on  the  macula;  and  if  the  image  of  B  is  above 
the  macula,  we  know  that  B  itself  is  below  A. 

The  table  on  page  116  is  suggested  as  a  guide 
in  cases  of  muscular  imbalance: 

Suppression  of  Image 
All  deviations  should  be  and  probably  are 
primarily  associated  with  diplopia.  Yet  in 
the  great  majority  of  cases  of  established 
squint,  especially  convergent  squint,  there  is 
no  double  vision.  This  is  due  to  the  mental 
suppression  of  the  image  by  the  squinting  eye. 
In  such  cases  all  attempts  to  evoke  diplopia  by 
our  tests  may  be  futile,  the  patient  not  appre- 
ciating the  presence  of  double  images  even 
when  they  are  widely  separated  by  prisms. 
Moreover,  this  suppression  usually  persists 
after  the  squint  is  cured,  so  that  even  though 
there  are  two  retinal  images  of  the  same  ob- 
ject, the  mind  perceives  but  one  and  ignores 
the  other,  just  as  though  it  were  not  present. 
In  this  case  there  is  no  true  stereoscopic,  or 
solid,  vision. 

Monocular  Diplopia 
Binocular  diplopia,  due  to  deviation  of  the 
eyes  or  to  prisms,  must  be  distinguished  from 

[115] 


M 

Q 
W 

H 
u 

w 

O 
u 

-o 

J. 

Ph  ^ 

Out  before   either 
eye. 

In  before  either 
eye. 

Down  before  right 
eye  or  up  before 
left  eye. 

Up     before     right 
eye  or  down  be- 
fore left. 

C 

'5 

Both  eyes  outward 
(divergence.) 

Both  eyes  inward 
(convergence.) 

Right   eye    down 
and    left   eye    up 

(left     supraver- 
gence.) 

Right  eye  up   and 
left   eye    down 
(right  supraver- 
gence.) 

< 

5^ 

In   before   either 
eye. 

Out    before    either 
eye. 

Up  before  right  eye, 
down    before    left 
eye. 

Down   before    right 
eye,  up  before  left 
eye. 

1 
"> 

3 
M-43 

Either  eye  inward    (eso- 
phoria,  esotropia.) 

Either      eye      outward 
(exophoria,     e  x  o  t  r  o- 
pia.) 

Right  eye  up  or  left  eye 
down   (right  hyperpho- 
ria,   right    hypertropia, 
left   hypotropia.) 

Right   eye   down   or   left 
eye  up    (left  hyperpho- 
ria,    left     hypertropia, 
right  hypotropia.) 

Image  of 
right  eye  as 

compared 
with  that  of 

the  left  is 

On  the 
right 

On  the 
left 

Below 
Above 

Name  of 
diplopia 

Homony- 
mous 

Heterony- 
mous (or 
-  crossed) 

'Right 

.Left 

|BJ3JBT                                      1BDI}J3A 

[116] 


Refraction    and   Muscular   Imbalance 

monocular  diplopia,  or  the  condition  in  which 
the  patient  sees  double  with  one  eye  alone. 
This  occurs  as  the  result  of  astigmatism,  plus 
spherical  aberration  and  other  conditions 
found  occasionally  in  squint.  It  can  readily 
be  differentiated  by  the  fact  that  binocular 
diplopia  disappears  when  the  patient  shuts 
either  eye;  while  monocular  diplopia,  of 
course,  does  not. 

Movement  of  Each  Eye  Singly 

The  movements  of  each  eye  individually 
are  effected  as  follows : 

The  external  rectus  moves  the  eye  directly 
outward ;  the  internal  rectus,  directly  inward. 

The  primary  action  of  the  superior  rectus 
is  to  raise  the  eye.  Because  of  the  way  in 
which  the  muscles  run,  obliquely  from  within 
outward,  its  lifting  action  increases  when  the 
eye  is  abducted  and  diminishes  to  little  or 
nothing  when  the  eye  is  adducted. 

The  inferior  rectus  carries  the  eye  down. 
Owing  to  the  oblique  direction  of  the  muscle, 
its  depressing  action  increases  as  the  eye  is  ab- 
ducted and  decreases  to  zero  as  the  eye  is 
adducted. 

The  inferior  oblique  is  inserted  back  of  the 
equator  of  the  eye.  Hence  it  pulls  the  back 
part  of  the  eye  down  and  consequently  throws 

[117] 


Refraction    and   Muscular   Imbalance 

the  front  part  up.  It  is  thus  an  elevator  of 
the  eye,  reinforcing  the  action  of  the  superior 
rectus.  Owing  to  the  way  in  which  it  runs, 
from  the  front  backward  and  outward,  its  ele- 
vating action  is  greatest  when  the  eye  is  ad- 
ducted,  and  diminishes  to  little  or  nothing 
when  the  eye  is  abducted. 

The  superior  oblique,  so  far  as  its  action  on 
the  eyeball  is  concerned,  may  be  regarded  as 
arising  from  the  trochlea.  From  this  point 
it  runs  backward  and  outward  and  is  inserted 
back  of  the  eq^uator  of  the  eye.  It  there  pulls 
up  the  back  part  of  the  eye  and  consequently 
throws  the  front  part  down.  It  is  thus  a  de- 
pressor, reinforcing  the  action  of  the  inferior 
rectus.  Owing  to  the  oblique  way  in  which 
it  runs,  its  depressing  action  is  greatest  when 
the  eye  is  adducted,  and  diminishes  to  little 
or  nothing  when  the  eye  is  abducted. 

Subsidiary  Actions 

Besides  these  actions,  rightly  regarded  as 
the  main  action  of  the  ocular  muscles,  there 
are  various  subsidiary  actions,  due  to  the 
oblique  way  in  which  the  superior  and  in- 
ferior recti  and  the  two  obliques  run.  Thus, 
both  the  superior  and  inferior  recti  adduct 
the  eye,  their  action  being  most  pronounced 
when  the  eye  is  already  adducted.     The  two 

[118] 


Refraction    and   Muscular   Imbalance 

obliques,  on  the  other  hand,  abduct  the  eye 
and  do  so  most  effectively  when  the  eye  is 
already  abducted. 

The  superior  rectus  and  superior  oblique  ro- 
tate the  top  of  the  vertical  meridian  of  the  eye 
inw^ard  (intorsion)  ;  while  the  inferior  oblique 
and  inferior  rectus  rotate  it  outward  (extor- 
sion) .  The  superior  and  inferior  recti  act  thu3 
on  the  vertical  meridian  mainly  when  the  eye 
is  adducted;  the  oblique,  on  the  other  hand, 
when  the  eye  is  abducted. 

Hence  the  eye  is  adducted  by  the  internal 
rectus,  assisted  toward  the  end  of  its  course 
by  the  superior  and  inferior  recti.  It  is  ab- 
ducted by  the  external  rectus,  assisted  toward 
the  end  of  its  course  by  the  two  obliques.  It 
is  carried  straight  up  by  the  superior  rectus 
and  inferior  oblique,  up  and  out  by  the  su- 
perior rectus  and  external  rectus  (the  inferior 
oblique  helping  to  carry  it  out,  but  not  up; 
and  in,  mainly  by  the  inferior  oblique  and  in- 
ternal rectus).  The  superior  rectus  assists 
in  carrying  it  in,  but  hardly  up  at  all. 

The  eye  is  likewise  carried  straight  down 
by  the  inferior  rectus  and  the  superior  oblique ; 
down  and  out  by  the  inferior  and  external 
recti,  and  down  and  in  by  the  superior  oblique 
and  internal  recti. 

[119] 


Refraction    and   Muscular   Imbalance 

Field  of  Action  of  Muscles 
As  will  be  seen,  each  muscle  acts  most  en- 
ergetically in  some  special  direction  of  the 
gaze,  termed  field  of  action  of  that  particular 
muscle;  thus  the  external  rectus  acts  most 
powerfully  when  the  eye  is  directed  outward, 
and  acts  little  or  not  at  all  when  the  eye  is 
directed  inward,  except  by  purely  passive  trac- 
tion. Likewise  the  superior  rectus  acts  main- 
ly when  the  eye  is  directed  down.  Further- 
more, its  action  is  limited  to  the  upper 
and  outer  field ;  for  in  the  upper  and  inner  field 
elevation  is  performed  chiefly  by  the  inferior 
oblique. 

This  is  also  true  of  all  the  other  muscles. 

Direction  of  the  Gaze 

There  are  six  cardinal  directions  of  the 
gaze,  each  corresponding  to  the  field  of  action 
of  one  of  the  six  ocular  muscles  as  follows : 

Cardinal  Direction:  Muscles  Specially  Active: 

Straight  out  External   rectus     . 

Straight  in  Internal  rectus 

Up  and  out  Superior  rectus    (as  an  elevator) 

Up  and  in  Inferior  oblique    (as  an  elevator) 

Down  and  out  Inferior   rectus    (as  a  depressor) 

Down   and  in  Superior  oblique   (as  a  depressor) 

It  is  to  be  noted  that  the  action  of  each  mus- 
cle does  not  absolutely  stop  at  the  middle  line, 
but  extends  somewhat  beyond  it.  Thus  the 
action  of  the  right  externus  extends  not  only 

[120] 


Refraction    and   Muscular   Imbalance 


throughout  the  whole  right  half  of  the  field 
of  vision,  but  also  some  fifteen  to  twenty  de- 
grees to  the  left  of  the  median  line;  and  that 
of  the  superior  rectus  extends  not  only  above 
the  horizontal  plane  but  also  somewhat  below. 

Primary  Position — Field  of  Fixation 
Under  normal  conditions,  when  the  head  is 
erect  and  the  eye  is  directed  straight  forward 
— that  is,  when  its  line  of  sight  is  perpendicu- 
lar to  the  line  joining  the  centres  of  rotation  of 
the  two  eyes  in  the  horizontal  plane — the  mus- 
cles are  all  balanced.  This  is  called  "the  posi- 
tion of  equilibrium"  or  the  primary  position. 
It  is  this  position  which  must  be  assumed  by 
the  patient  in  conducting  tests  for  balance  of 
the  muscles. 

From  the  primary  position,  the  eye  may 
make  excursions  in  every  direction  so  that  the 
patient  can  look  at  a  whole  series  of  objects 
in  succession  without  moving  the  head.  This 
portion  of  space,  occupied  by  all  the  objects 
that  may  thus  be  seen  directly  by  moving  the 
eye  without  moving  the  head,  is  called  "the 
field  of  fixation." 

Binocular  Movements 
While  either  eye  alone  may  move  in  all  pos- 
sible directions,  one  cannot  move  independent- 
ly of  the  other  eye.    Under  ordinary  circum- 

[121] 


Refraction    and   Muscular   Imbalance 

Stances,  those  movements  only  are  possible 
which  are  regularly  required  to  subserve  bi- 
nocular vision,  hence,  binocular  single  vision, 
as  well.    These  movements  are  as  follows: 

Parallel  Movements 

When  one  eye  looks  at  a  distant  object  the 
other  is  also  directed  to  it,  so  that  the  lines  of 
sight  of  the  two  eyes  are  parallel ;  if  the  distant 
object  is  moved  about,  the  lines  remain  paral- 
lel, one  moving  as  fast  and  as  far  as  the  other. 
These  parallel  movements  of  the  two  eyes  are 
executed  with  considerable  freedom  in  all  di- 
rections, either  eye  being  able  to  move  read- 
ily to  the  right,  left,  up,  down,  or  obliquely, 
provided  the  other  eye  moves  precisely  with  it. 

In  executing  any  parallel  movement,  each 
eye  is  acted  upon  by  at  least  three  and  some- 
times by  as  many  as  five  muscles.  At  times, 
but  one  of  these  muscles  is  required  to  pro- 
duce any  great  movement  of  the  eye,  the  others 
simply  serving  to  steady  it  in  its  course.  Thus 
when  we  look  up  to  the  right,  although  there 
are  five  muscles  really  acting  upon  each  eye, 
the  right  eye  is  moved  mainly  by  the  external 
rectus  and  the  left  eye  by  the  internal  rectus. 

Similarly,  when  we  look  up  and  to  the  right, 
although  other  muscles  take  part,  the  superior 
rectus  is  the  chief  muscle  that  moves  the  right 

[122] 


Refraction    and   Muscular   Imbalance 

eye  up,  and  the  external  rectus  the  chief  one 
that  moves  it  to  the  right;  while  for  the  left 
eye  the  interior  oblique  and  the  internal  rec- 
tus are  the  efficient  muscles. 

A  careful  study  of  the  action  of  the  indi- 
vidual muscles  will  make  it  clear  that  these 
facts  hold  good  for  each  of  the  cardinal  direc- 
tions of  the  gaze. 

Furthermore,  if  we  attentively  consider  the 
action  of  the  twelve  muscles  moving  the  two 
eyes,  we  see  that  they  may  be  divided  into 
three  groups,  viz;  four  lateral  rotators,  four 
elevators  and  four  depressors. 


Right  rotators 

L.    Internal    rectus 

R.  External  rectus 


Lateral  Rotators 

I  fLeft  rotators 

-{  R.  Internal  rectus 
I  L.  External  rectus 


to 


Elevators 


Right-handed  elevators 

(acting  mainly  when  the 

eyes  are  directed  to  the 

right) 

R.  Superior  rectus 

L.   Inferior   oblique 


Right-handed  depressors 

(acting  mainly   when   the 

eyes    are    directed    to    the 

right) 

R.  Inferior  oblique 

L.  Superior  oblique 


Left-handed  elevators 

(acting  mainly   when   the 

eyes    are    directed    to    the 

left) 

R.  Inferior  oblique 

L.  Superior  rectus 


Depressors 


Left-handed    depressors 

(acting   mainly   when    the 

eyes    are   directed   to  the 

left) 

R.  Superior  oblique 

L.  Inferior  rectus. 


Each  group,  it  will  be  seen,  comprises  two 
pairs  of  muscles;  one  pair  acting  solely  when 


[123] 


Refraction    and   Muscular   Imbalance 

the  eyes  are  directed  to  the  right,  the  other 
when  they  are  directed  to  the  left.  It  will 
further  be  noted  that  of  the  two  muscles  con- 
stituting any  one  pair,  one  is  situated  in  the 
right  eye,  the  other  in  the  left. 

Eye  Associates 

The  muscles  forming  any  one  pair  are 
called  associates.  Any  two  associates  acting 
together  will  move  their  respective  eyes  in 
precisely  the  same  direction  and  to  the  same 
extent.  Thus  the  right  superior  rectus  moves 
the  eye  up  to  the  left  and  rotates  its  vertical 
meridian  to  the  left;  and  its  associate,  the  left 
inferior  oblique,  moves  its  eye  up  to  the  left 
and  rotates  its  vertical  meridian  to  the  left. 
This  likewise  applies  to  each  of  the  other  five 
groups  of  associates. 

If  one  eye  fails  to  keep  pace  with  the  other 
in  executing  parallel  movements,  diplopia  en- 
sues. If  the  eyes  are  moved  in  all  directions 
and  the  point  noted  where  the  patient  just  be- 
gins to  see  double,  we  delimit  the  field  of  bi- 
nocular single  vision. 

Normally,  however,  the  two  eyes  maintain 
parallelism  to  the  very  limit  of  their  excur- 
sion, so  that  diplopia  occurs  only  at  the  ex- 
treme periphery  of  the  field  of  vision,  if  at  all. 
In  fact,   the  field  of  binocular  single  vision 

[124] 


Refraction    and  Muscular   Imbalance 

usually  extends  not  less  than  40  degrees  from 
the  primary  position  in  every  direction. 

Each  of  the  various  parallel  movements  of 
the  eye  appear  to  be  governed  by  a  distinct 
nerve  mechanism,  there  being  one  centre  for 
movements  to  the  right,  one  for  movements 
to  the  left,  one  for  movements  up,  etc. 

Movements  of  Convergence 

In  order  to  see  an  object  at  a  nearby  point, 
the  eyes  have  to  converge — a  movement  af- 
fected by  a  simultaneous  and  equal  contrac- 
tion of  both  internal  recti.  This  movement 
may  be  combined  with  a  vertical,  lateral  or 
oblique  parallel  movement.  Thus,  when  we 
wish  to  look  at  a  near  object  situated  twenty 
degrees  to  our  right,  we  first  turn  both  eyes 
twenty  degrees  to  the  right,  then  converge 
both  equally,  turning  the  left  a  little  more  to 
the  right  and  the  right  a  little  back  toward  the 
left. 

Convergence  is  governed  by  a  distinct 
mechanism  of  the  nerves,  the  source  of  which 
has  not  been  determined. 

Movements  of  Divergence 

In  passing  from  a  position  of  convergence 
to  a  position  of  parallelism,  the  lines  of  sight 
separate  or  diverge.    This  movement  of  diver- 

[125] 


Rcfnictioii    and    Muscular    Iiuhalance 

gence  is  a  simultaneous,  equal  contraction  of 
both  externi;  or,  probably,  of  both  actions 
combined.  The  eyes  may  even  diverge  some- 
what beyond  parallelism,  as  in  overcoming 
prisms,  base  in,  when  looking  at  a  distant  ob- 
ject. 

Vertical  Divergence 

The  amount  by  which  the  lines  of  sight 
can  separate  in  a  vertical  direction  is  very  lim- 
ited^ — at  most  but  one  or  two  degrees. 

Orthophoria 

The  term  orthophoria  is  used  to  denote  an 
absolutely  normal  balance  of  the  extrinsic 
muscles,  just  as  the  term  emmetropia  denotes 
a  normal  refractive  condition.  They  are 
equally  rare. 

Heterophoria 

The  term  heterophoria  includes  all  those 
conditions  in  which  there  is  a  tendency  to  de- 
part from  normal  balance,  but  which  nature 
is  able  to  compensate  for;  while  the  term  also 
includes  the  conditions  in  which  nature  has 
been  unequal  to  the  task  and  an  actual  turn- 
ing or  squint  has  occurred. 

Subdivisions 

The  subdivisions  of  these  terms  at  first  read- 
ing   appear    complicated,    but    prove    simple 

[126] 


Refraction    and   Muscular   Imbalance 

enough  on  closer  study,  indicating  only  the  di- 
rection of  the  turning  or  tendency  to  turn. 
For  instance : 

Esophoria  signifies  imvard  tendency 
Exophoria  signifies  outivard  tendency. 
Hyperphoria  signifies  upivard  tendency. 
Hypophoria  signifies  doivriivard  tendency. 
Cyclophoria  signifies  tendency  to  torsion. 
Esotropia  signifies  imvard  turning. 
Exotropia  signifies  oi/tivard  turning. 
Hypertropia  signifies  upivard  turning. 
Hypotropia  signifies  doivntvard  turning. 
Cyclotropia  signifies  actual  torsion. 

Combinations  are  describable  in  similar 
terms.  A  tendency  of  the  right  eye  to  turn 
up  and  inward,  is  a  ''right  hyperesophoria" ; 
the  left  eye  to  turn  down  and  out,  a  ''left  hy- 
perexophoria,"  etc.  Tendencies  of  both  eyes 
together  are  denoted  by  the  terms  which  fol- 
low: 

Anaphoria  signifies  an  upivard  tendency. 
Kataphoria  signifies  a  doivnivard  tendency. 
Dextrophoria  signifies  a  riff/it  tendency. 
Laevophoria  signifies  a  left  tendency. 


[127] 


Chapter  XVII 

SYMPTOMS  OF  HETEROPHORIA 

npHESE  depend  on  the  kind  of  error  pres- 
ent as  well  as  the  degree  and  widely  vary. 

In  general,  they  may  be  said  to  fall  into 
three  classes — (1)  defective  vision,  (2)  pain 
of  greater  or  less  degree — (3)  reflex  symp- 
toms. 

Defective  Vision.  The  first  class  may  be 
present,  even  though  each  eye  has  a  normal 
visual  acuity;  since,  even  when  compensation 
is  very  good,  the  brain  gets  the  impression  of 
two  objects,  nearly,  though  not  quite  fused; 
and  vision  may  be  considerably  worse  with 
both  eyes  together  than  with  either  eye  singly. 

When  compensation  is  considerably  im- 
paired, the  diplopia  becomes  more  and  more 
persistent,  till  the  brain  finally  makes  choice 
of  one  image  as  more  satisfactory,  entirely 
suppressing  the  other.  Visual  acuity  may  not 
suffer  in  either  eye;  but  vision  being  no  longer 
binocular,  everything  is  seen  in  the  flat,  the 
judgments  of  depth  and  distance  being  regu- 
larly more  or  less  defective.  While  this  is 
a  tremendous  disadvantage  in  many  occupa- 
tions, people  gradually  and  not  infrequently 
become  accustomed  to  these  visual  defects  and 
are  not  conscious  of  the  handicap. 

[128] 


Refraction    and   Muscular   Imbalance 

Pain.  It  is  quite  different  with  the  second 
set  of  symptoms,  which  are  always  accompan- 
ied with  pain.  In  fact,  the  character  of  the 
subjective  symptoms  in  refractive  errors  and 
muscular  imbalance  is  so  similar  that  it  is 
practically  impossible  to  differentiate  in  many 
cases. 

In  muscular  asthenopia,  however,  in  addi- 
tion to  becoming  easily  tired,  the  patient  often 
complains  that  letters  seem  to  jump  or  run 
together  or  he  may  contend  that  he  sees  double 
for  an  instant;  or  again  that  he  can  "feel  his 
eyes  turn"  involuntarily  in  their  sockets. 
These  pains  or  conditions  are  sometimes  pres- 
ent only  during  actual  use  of  the  eyes.  At 
other  times  they  persist  for  hours.  In  some 
cases,  after  days  or  weeks  of  overstimulation, 
an  explosion  in  migraine  form  occurs  at  ir- 
regular intervals.  This  condition  often  lasts 
a  day  or  two. 

Reflex  Symptoms.  In  the  third  and  last 
case,  there  are  other  reflex  symptoms — such  as 
dizziness,  nausea,  fainting,  indigestion,  in- 
somnia and  pains  in  other  portions  of  the  body 
— sometimes  stimulating  organic  diseases. 

The  possibility  of  heterophoria  as  a  factor 
in  chorea,  migraine,  neurasthenia  and  other 
diseases  which  may  be  primarily  due  to  un- 
stable nerves,  equilibrium  is  not  to  be  forgot- 

[129] 


Refraction    and   Muscular   Imbalance 

ten.  It  is  a  notable  fact  that  when  the  fusion 
compensation  fails  so  completely  that  one 
image  is  entirely  suppressed,  or  the  diplopia 
is  so  great  as  to  be  overlooked,  the  symptoms 
often  cease  entirely. 

Treatment 

The  treatment  of  heterophoria  depends  on 
a  careful  study  of  each  individual  case, 
but  it  cannot  be  too  strongly  emphasized 
that  in  the  great  majority  of  cases  the  sub- 
jective symptoms  disappear  after  a  full  cor- 
rection of  the  refraction  is  made. 

In  many  cases,  if  the  visual  acuity  in  each 
eye  be  made  normal,  the  fusion  impulse  alone 
W\\\  be  sufficient  to  restore  compensation. 

Many  cases  of  csophoria  result  from  over- 
stimulation of  the  centers  for  convergence  and 
accomodation,  made  necessary  by  hyperopia 
and  astigmatism,  entirely  disappearing  when 
glasses  abolish  the  need  of  accomodation. 
Cases  of  exophoria  are  sometimes  due  to  the 
abnormal  relaxation  of  accomodation  and  con- 
vergence which  secures  the  best  distant  vision 
in  myopia.  Likewise  the  correction  of  my- 
opia, by  increasing  the  far  point,  may  dimin- 
ish the  amount  of  convergence  necessary  for 
near  vision. 

[130] 


Refraction    and    Muscular    luihalance 

Prisms  for  constant  use  are  often  prescribed, 
so  placed  as  to  help  the  weak  muscles  and 
counteract  the  strong.  For  instance,  in  eso- 
phoria  we  find  the  prism  which,  base  in,  will 
produce  orthophoria  for  distance  and  pre- 
scribe a  quarter  of  it,  base  in,  before  each  eye. 
While  this  is  very  successful  in  some  cases, 
the  tendency  in  others  is  for  the  externus  to 
increase  slightly  from  constant  exercise  in 
overcoming  the  prism,  while  the  internus  de- 
creases in  proportion  to  the  amount  of  work 
of  which  it  is  relieved.  Prisms  for  perma- 
nent use  are  very  beneficial  in  vertical  devia- 
tions, since  when  the  images  are  brought  on 
the  same  level  they  require  much  less  efifort 
to  secure  fusion;  and  when  prescribed  base  up 
or  down,  the  effect  secured  is  commonly  an 
unchanging  one. 

We  sometimes  take  advantage  of  this  ten- 
dency when  we  prescribe  for  constant  use 
weak  prisms  with  the  apex  over  the  weak 
muscle,  which  gradually  becomes  strong  from 
the  exercise  of  overcoming  it.  This  plan 
is  effective  only  in  patients  who  have  a  strong 
fusion  impulse,  and  the  prism  selected  must 
be  weak  enough  to  be  easily  overcome.  We 
can  accomplish  the  same  effect  by  decentering 
the  patient's  refraction  lenses. 

For  instance,  a  convex  lens  so  placed  that 

[131] 


Refraction    and   Muscular   Imbalance 

the  visual  line  passes  the  reverse  will  be  the 
case  if  the  lens  is  concave.  The  amount  of 
prismatic  action  depends  on  the  strength  of 
the  lens  and  the  amount  of  decentering,  the 
rule  being  that  every  centimeter  of  displace- 
ment causes  as  many  prism  dioptres  as  there 
are  dioptres  in  that  meridian  of  the  lens.  Thus 
+  1  sphere,  or  cylinder  axis  90,  decentered  one 
centimeter  outward,  is  equivalent  to  adding  a 
one  degree  prism  dioptre  lens,  base  out. 

Destrophoria   and    Laevophoria 

These  are  terms  denoting  a  condition  in 
which  both  eyes  are  capable  of  abnormal 
rotating  toward  the  right  or  left,  as  the  case 
may  be.  The  movement  in  the  opposite  di- 
rection is  most  common.  The  patient  can  often 
rotate  his  eyes  60  degrees  toward  the  right, 
and  to  perhaps  only  40  degrees  to  the  left.  His 
position  of  rest  is  parallel  with  his  visual  lines, 
but  to  the  right,  in  looking  at  objects  directly 
in  front,  he  is  much  more  comfortable  with 
his  head  turned  slightly  to  the  left. 

It  is  difficult  to  account  for,  except  on  the 
theory  that  definite  movement  of  the  eyes  is 
rather  to  the  right  than  to  the  left  in  most 
occupations.  The  position  of  the  paper  in 
writing  at  a  desk  tends  toward  dextrophoria; 
in  reading,  we  move  our  eyes  steadily  from 

[132] 


Refraction    and   Muscular   Imbalance 

left  to  right  and  then  begin  a  new  line  by  a 
single  brief  movement  to  the  left;  the  things 
that  a  man  uses  most — whether  he  be  laborer 
or  student — are  kept  within  reach  of  the  right 
hand,  and  in  referring  to  them  the  eyes  are 
constantly  turned  toward  the  right. 

However,  when  these  conditions  result  from 
other  imbalances,  they  must  be  treated  more 
carefully.  For  instance,  a  patient  whose  right 
internus  is  paralysed  or  congenitally  defec- 
tive on  looking  to  the  left,  has  a  cross  diplopia 
which  vanishes  to  the  right;  as  a  result,  he  soon 
assumes  a  habit  of  carrying  his  head  in  this 
position.  Ordinarily,  this  will  cause  no  dis- 
comfort; but  if  the  left  internus  is  so  weak  that 
it  cannot  follow  the  right  externus  to  its  posi- 
tion of  greatest  ease,  the  visual  lines  are  evi- 
dently different  and  the  case  must  be  treated 
as  an  exophoria. 

If,  on  the  other  hand,  the  left  internus  over- 
balances the  right  externus,  the  condition  is 
an  esophoria  and  must  be  treated  as  such. 

Similar  reasoning  applies  to  the  conditions 
known  as  Anaphoria  and  Kataphoria,  in 
which  the  visual  lines  are  parallel  to  each 
other  but  directed  up  or  down  with  regard  to 
the  horizontal  plane  of  the  body. 

In  the  first,  owing  to  congenital  abnormali- 
ties, the  eyes  usually  tend  upward  and  the  in- 

[133] 


Rcf  raft  ion    and   Muscular    Imbalance 


dividual  must  go  about  with  his  chin  on  his 
chest,  so  that  his  eyes  may  look  in  front  and 
yet  remain  in  the  position  of  rest.  In  the 
second,  the  chin  is  held  in  the  air  and  the  body 
arched  backward. 

But,  unless  extreme,  neither  of  these  condi- 
tions causes  more  than  cosmetic  difficulty  and 
both  should  be  undisturbed  owing  to  the  ex- 
treme difficulty  of  securing  the  same  opera- 
tive effect  on  both  eyes.  Suitable  prisms  are 
much  more  likely  to  be  beneficial. 


34] 


Supports  for  Holding 
The    Ski-optometer 


Floor  Stand 


Choice  may  be  made 
from  any  of  the 
above.  The  Wall 
Bracket  is  recom- 
mended, unless  re- 
fractionist  is  provided 
with  a  specialist's 
chair,  to  which  the 
Chair  Attachment 
with  Upright  may 
be   attached. 


[135] 


14  DAY  USE 

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